Autofocus is one of the most useful advances in modern photography. Most modern video surveillance systems cannot be imagined without autofocus. Learning to control this technology is one of the most important skills for any photographer.

What is autofocus?

To begin with, it would be nice to answer another question. What is focus? In photography, this concept is central, it refers to an image with high definition, originality, some small details. Achieving precise focus is what photographers usually strive for.

Having a camera in our hands, as a system with perfect vision, we see the object of our interest - a display with perfect detail. Just like with poor eyesight, with poor focus, the world appears blurry. Fortunately, unlike our eyes, the focus of the lens can be adjusted to get the sharpness you want, however, this is not easy and even not always possible. This is where autofocus comes in.

At its core, autofocus is any technology that automatically (without the intervention of the photographer) changes the focal length of the lens. This feature can be more precise than "eye" control and manual focus, and can be used to improve focus on moving objects that our eyes and reflexes struggle to track.

Using autofocus

Most people are already familiar with autofocus. It exists on almost all modern cameras, from advanced format Hasselblads to regular smartphones, and is almost always set to default focus. Simply put, no autofocus - no confidence in what you're doing.

Don't you think it's strange that after buying a fancy DSLR, autofocus seems less flexible than on a phone? With smartphones, everything is simple, you press the button with your finger, you get a nice little picture, and everything that gets into the frame can be seen very clearly. What a nice trick.

This is the viewfinder screen of the D3100, which has an 11-point autofocus system. More advanced cameras currently work up to the 61st autofocus point.

Looking at a DSLR, you think, well, what a hassle, limited to the number of points in the viewfinder! Without going into unnecessary details, let's just say that DSLRs use a different autofocus method than digital cameras and smartphones, for which it is not particularly necessary to process what the lens sees.

This may seem like a drawback at first glance, but this autofocus mode is faster and more accurate. In this article, we will pay special attention to the autofocus system on digital SLR cameras instead of smartphones (if you want to read about the iPhone, Google it).

Now that we know that we rely on fixed points, it's time to learn about two key issues. How to choose the right moment and what happens if the focus does not stop at the object we need?

Autofocus vs. Manual focus

First, we need to see what mode is selected in the menu. Most of the modes belong to the so-called "auto-scenes", where the camera settings change depending on the type of shooting you choose. Naturally, these modes involve autofocus (there are, of course, exceptions, such as macro mode).

For example, in a DSLR camera, the main mode is autofocus. When you press the shutter button, you kind of give a signal to highlight certain points on the viewfinder. These focus points are a reflection of how the camera sees the subject. If this is not what you were trying to film, then you are out of luck.

In order to independently control the autofocus on a DSLR, you need to use one of the "manual" modes (P, A/AV, S/Tv or M). In these modes, the focus point can be selected manually. Focusing accuracy varies from model to model. But usually DSLRs are similar in this. "Manual" mode will help you if you want to take full control of the shooting.

Of course, you can do otherwise, but most photographers stick to this method. To focus on objects in the center, you must be attentive. This is the easiest way to get an image in focus and can be achieved in three steps.

Step 1.

Focus mode - one shot. Set the focus point to the center of the viewfinder. The middle AF point will line up with it, and the image will come out much sharper.

Step 2

The point should be directly on your subject, press the shutter button halfway for the so-called pre-focusing. Once this is done, your camera's AF LOCK will clearly "see" what you want to shoot, what the focal length is to the subject, and will remember it even if you move the camera.

Step 3

With the focal length decided, now you have complete freedom in the frame. Normally still subjects are pretty boring for photos, but when you're happy with the composition, press the shutter button all the way down.

We use the center button on autofocus to focus on the subject for the first time, then after AF lock, we can create freely. This is called pre-focusing.

Choose a focus point manually.

It's rare to have a focal point exactly where you want it, even with the new 51-point systems. So if we have the ability to recompose after pre-focusing, what's the point of extra points?

The first reason is that there may be times when it is physically impossible to change the composition. While the "focus and create" method is great for most situations, there are times when the most precise focusing is needed and no amount of "by eye" is appropriate.

In such situations, having a flexible multi-point autofocus system becomes very useful.

The main purpose of such systems, however, is not to save time. The goal is rather to give the photographer the ability to capture moving subjects. This is especially important for shooting wildlife and sports photographers, for them the ability to properly use autofocus is crucial, as it is for everyone who shoots dynamic objects.

Let's say you want to take a photo of a running child. By the time you set the focus, the child will be long gone (forget about trying to recompose after focusing first in this case).

Even with the very fast autofocus of today's systems, there is no way to take more than one shot at a time without changing the focus paradigm. How can you use a high shooting speed so that you can then select one of the consecutive frames?

Most DSLR cameras support, in addition to the aforementioned one-shot autofocus feature, a very powerful feature called continuous autofocus (AF-C in Nikon and AL Servo in Canon).

How does it work in general, that immediately after the system has been focused on the first frame, the movement of the object will be tracked, and moreover, auto focus will be selected almost immediately!

This will continue as long as the shutter button is pressed halfway and held. During use, the camera will adjust the lens to maintain focus on the subject by predicting how the subject will use its speed.

This way you can take a series of photos in quick succession without worrying about focus and maximize the chance of getting the best shot.

The tip that was the most important for me when I learned to shoot with autofocus. Because autofocus is done with sensors that detect it, this only works well when the focus point is in some sort of contrast!

For example, when I set the AF point to the edge of the subject, the focus is instantaneous and very accurate. But if I try to point it towards the middle of the object, where the tone and color are constant, the sensor can't determine how sharply it sees it.

Think about it, the sensor only has the information it uses to determine focus. It's like looking through a straw and trying to figure out if your eyesight is perfect or not. This is only possible when you can see the edges of objects, not when there is only a white wall around.

To make it reuse the previously selected focus, you can see what happened when I tried to focus on two different points directly. The left image will be more accurate as there is a sharp contrast between the flash drive and the background. The right one will not be as accurate, because the contrast is not so strong. (In general, the camera won't let you take a picture until the sensors are sure it's in focus).

Most DSLRs have an AF light that can be turned on on some models. It helps to focus in the dark. If everything is black around, the camera is facing the same problem as in tip #1, the sensor has no idea what is in focus and what is not. Note, however, that this mode should not be enabled in places where flash photography is prohibited.

As it may seem, this is the solution to most problems, gave money - got an easy way to improve autofocus. Fast - that is, having a maximum aperture (smaller aperture value, for example, f / 1 / .8), that is, the lens has a larger aperture.

When the camera tries to autofocus, it always opens the aperture as wide as possible to let in as much light as possible, according to the settings, of course. The greater the maximum aperture potential of the lens, the easier the autofocus process will be.

In fact, when using low-end DSLRs with small apertures, such as f / 5.6 lenses, usually kit lenses, autofocus will not work at any points other than the center, even pro-class cameras can only cope with lenses of high maximum aperture potential diaphragm.

How does autofocus work on a smartphone? What type of autofocus works best? Pros and cons of laser, phase and contrast AF. Why is dual-pixel so good?

How does autofocus work on a smartphone? There is no simple answer to this question. It is necessary to deal with each type of autofocus, to study the features of a particular focusing technology. Only then can any conclusions be drawn. Therefore, now we will talk about the varieties of auto focus technologies, and about the advantages and disadvantages of each of them.

What is camera focus and autofocus

Everything is simple here: the lens of the lens refracts the rays and collects all the light at one point - the focus. And if the matrix sensor is located at this point, then the frame is more detailed and of high quality. Naturally, all photographers use this physical phenomenon. They bring some part of the frame into focus, adjust the lens manually and focus the viewer's attention on the foreground or background, the main subject or a minor detail. The rest of the picture will be blurry.

Well, novice photographers can use the auto focus system, when the automation captures one or more objects in the frame “in focus”, controlling both the lens and the matrix. And these objects (or object) are as sharp and detailed as possible. And no skill and sense of the frame is no longer needed here.

This is probably why digital photography has become more popular than the film-and-paper version of art. After all, autofocus in the camera of a phone or a cheap camera allows you to take a detailed picture without any extra effort. The whole process boils down to a simple rule: point and click.

Varieties of autofocus and the basic principles of their work

The camera lens focuses the rays reflected from an object located in the space in front of the lens. When focusing, the camera focuses on the distance to the object and on the intensity of the glow emanating from it. Today, there are two types of auto focus modes:

1. Active option - it is based on measuring the distance using a rangefinder locator.
2. Passive option - it works with a light beam, measuring its intensity.

The first (active) mode uses laser infrared or ultrasonic radiation with a known speed of wave propagation in air. The emitter module emits a directed stream, which is reflected from the object and is captured by the receiver module after a certain period of time. The autofocus calculator then multiplies this time by the known wave propagation speed and divides the result by two to get the exact distance. By directing the emitter to the desired area, the user receives optimal focus, focusing the viewer's attention on this particular area of ​​the photo.

The second (passive) mode is arranged somewhat differently. It uses special sensors (photodiodes) that measure the intensity of the glow and a special processor that determines the focus by the value of this parameter. In practice, it looks like this: the sensors record the intensity of the glow, then the processor shifts the focus, after which the intensity is re-measured, if the flux density has increased, then the focus is considered acceptable. If not, the focus is shifted again. And so on until the maximum intensity is found. There are up to 40-60 photodiodes in the matrices of serious cameras.

Based on these principles, the most famous focusing systems work: phase, laser, contrast and dual-pixel. And further in the text, we will evaluate each option along the way, evaluating their basic advantages and disadvantages.

Advantages and disadvantages of laser autofocus

In this case, a laser emitter and receiver are built into the phone camera model. The first generates a narrow beam, the second receives the reflected signal. As a result, the speed of focusing is reduced to thousandths of a second. Usually we are talking about 250-300 milliseconds, since the laser propagates at the speed of light.

The main advantage of the laser focus is the high reaction speed of the module, and the main disadvantage is frequent failures. A narrowly focused laser emitter sometimes "shoots" past the target, and the reflected signal is easily lost, especially in open spaces. Therefore, laser autofocus in a smartphone camera in most cases works in tandem with a phase or contrast guidance option.

Features of phase focusing

The technology is based on splitting the beam passing through the lens into two streams. This is done in order to measure the distance between streams passing through opposite edges of the lens. If this distance is within certain values ​​specified in the data array, the picture is considered to be focused. To fix the distance, special sensors are used that react to light. Their signals are processed by the processor, which compares the read parameters with the base data array and gives a signal to shift the focus in the right direction.

The main advantage of the technology is the willingness to focus on a moving object. In addition, this option is faster than contrast autofocus. And this system can also be used to calculate such a parameter as depth of field.

The main disadvantage of phase technology is its complex implementation. The system of prisms, mirrors, lenses requires ultra-precise physical alignment and no less scrupulous program settings. In addition, the accuracy of such a focus depends on the lens aperture, and mobile phones have big problems with this parameter.

Pros and cons of contrast focus

The technology does not change either the matrix or the optical system of the smartphone camera. Either the entire photosensor or part of it is used as a sensor. The processor reads the current histogram from the sensor and evaluates the contrast of the frame. And then the lens is given a command to shift the focus, after which the histogram is read again with a reassessment of the contrast. And the whole cycle is repeated until the maximum level of contrast is reached in the selected area of ​​the frame, which is focused.

The main advantage of the technology is a combination of ease of implementation, low cost of construction and compact size. Such autofocus is used by all manufacturers of budget smartphones.

The key disadvantage of this option is the very slow speed. Sometimes the processor goes into the eternal “hunting for focus”, which ends in the loss of a rare frame.

Dual Pixel technology

This focusing technology is used in expensive SLR cameras. In mobile devices, it is still used only in Samsung's flagship models, deliberately lowering the resolution of the photographic matrix while increasing its physical dimensions.

These tricks are due to the desire to attach an individual sensor to each pixel of the photographic sensor, which reacts to the intensity of the glow. Then the signals from the sensors are processed according to both the phase and contrast focusing algorithms, achieving not only a perfectly sharp, but also the most contrasting image.

If in the case of the classic phase focus, the sensors account for no more than 10% of the total number of pixels in the camera, then in the case of the Dual Pixel they are divided in a 50/50 ratio. Simply put, each pixel is a photosensitive element and a sensor at the same time. This technology provides more accurate and faster focusing.

Of the disadvantages of Dual Pixel, it should be noted that such solutions are very difficult to implement. Only flagship devices are equipped with such tricks, for example, devices from the Samsung S-series (from the seventh model and higher). There is something similar in the latest iPhones (from the sixth model and up), but Apple calls this focusing technology Focus pixels, and it is closer to conventional phase detection autofocus than to Dual Pixel.

The most common complaints I hear from most photographers of any level are "my images aren't sharp" and "I can't get focus." Many people blame their equipment and, indeed, there are many cases in which the equipment is to blame. However, I have found that the vast majority of cases are simple user errors. They often boil down to a lack of understanding of how the autofocus (AF) system works. This article will give you a better idea of ​​focus and sharpness, and hopefully help you get photos you're happy with!

1. Adjust your diopters

What are mine, you ask? Your diopters - or your eyepieces. You will never know if a camera is well focused on a subject unless you can see for yourself what is in focus through the viewfinder eyepiece. On the side of the eyepiece (as shown below) there is a small wheel to adjust the focus of the eyepiece to suit your vision.

You can adjust the eyepiece to quite a large correction, but if you need even more correction, then interchangeable diopters are available for DSLR / SLR cameras from many major manufacturers in the range from -5 to +4. No, this won't help your autofocus work better, but it will help you recognize when it misses and correct the situation with manual focus.

2. Understand your viewfinder

What the hell do all these things inside mean? At this point, you might want to get the instructions (remember that paper book that came with your camera?). Most conventional DSLR cameras have 9-11 focus points. The best of the best, professional cameras can have from 45 to 51 points (although in fact you can only choose 11-19, the rest of the points are optional).

There are two types of focus points: co-plane and intersection points. Single plane points only work on contrast lines that are directly perpendicular (90°) to their orientation. So, if you're looking through your viewfinder like the one above, you'll see that most of the dots are rectangular, some are oriented horizontally, some are oriented vertically.

Points of the same plane will only work perpendicular to their orientation. So - let's say you were shooting a tree - a vertical focus point wouldn't be able to find the edge of the tree trunk, but a horizontal one would. You can use this to your advantage when choosing a focus point that will lock onto the line you want and ignore those you don't want to focus on.

Cross point focus points will work with lines of contrast placed in any way. Most cameras have a single focusing intersection point in the center, surrounded by points on the same plane. The newest cameras today contain intersection points at all focal points.

Each focus point also has a specific sensitivity. Most require a lens with an aperture limit of at least f5.6 to even use autofocus. On most cameras, the surrounding AF points are just that sensitive, and the center point provides increased sensitivity if you use a lens with an aperture limit of at least f2.8.

So if you're working in low light conditions, you can achieve better autofocus by using the center focus point. Even if you don't use an f2.8 lens, or better yet, there are no light restrictions to favor the center point, it can still give a more accurate result because it is the intersection point.

When we look at the focus point rectangles, it's worth remembering that the real area of ​​the sensor is 2-3 times larger than what is displayed. Keep this in mind as you focus. If you fix the focus on someone's bridge of the nose, remember that the person's eyes will also fall into the active area of ​​the sensor. Autofocus will lock on to the eye rather than the bridge of the nose because the eye has more edge contrast than flat lighting on the nose. Often this may not matter, but if you are working at a very shallow depth of field, you will feel the difference in which area of ​​the image is most sharp.

3. Lend a helping hand to your lens

Most autofocus systems have a certain amount of error or variance and can actually miss the point of optimum focus due to the mechanics and inertia of lens movement. You can minimize this effect by manually focusing the lens as close to the desired focus as possible, and then let the autofocus system finish focusing. Or, if this seems too difficult for you, at least let the autofocus make two attempts to achieve correct aiming. Half-press the shutter button to set the approximate focus, and then press again to fine-tune it.

The advantage of higher end lenses is that they allow full manual control even when autofocus is locked. Cheaper lenses don't allow you to manually adjust the focus after locking, although this is a good way to make sure the focus is as perfect as can be.

4. Find a good line

Autofocus systems work on contrasting lines, so they may struggle on non-contrasting subjects (eg cheek or forehead, white dress or black tuxedo, sand, monochrome walls, etc.). In areas like these, autofocus can go all day long and never lock. The approach is to find the "best line" - it could be the eyes, the lines between the contrasting shirt and suit, between heaven and earth, the doorway. Anything with contrast will help autofocus work better and faster.

Weak focus zone

Best Area to Focus

5. Don't use all-point focus mode

Unless you're in a terribly fast-paced situation that requires incredibly fast aiming, it's best to avoid all-point focus mode. This mode doesn't know what you want to focus on and is usually fixed to whatever is closest to the camera. There are situations in which this is exactly what is needed, but they are few and far between.

6. Focus and recompose - but do it the right way

I'm used to focusing and recomposing using the center focus point all the time. I lock the focus and then recompose the shot. I once read a few articles that said you shouldn't do this - that you should use the point closest to the area you want to focus on. Theoretically, this is justified by the fact that during the movement of the camera, due to the movement of the lenses and the change in the angle value, the distance between the subject and the lens also changes.

If you use the focus point directly on the subject and do not recompose the frame, then there will be no change in the distance between the subject and the lens, and therefore erroneous focusing. So, I decided to take some pictures to show you that it is - and it is not.

There was absolutely no advantage in using the nearest non-center point without changing the composition. In fact, focusing using the center point and recomposing was, indeed, more accurate in all cases except for one - macro. I took shots at all focal lengths from 17mm to 200mm and checked all distances from macro to 10 meters - with the same results.

Each test using the center focus point and recomposing the frame resulted in a sharper picture. Greater sharpness from using the center point and recomposing, less sharpness from using an outer focus point right on the subject. To clarify, the above theory is correct, in that you lose sharpness by moving the frame away from a fixed center point. What's not true is that using an outer point directly on the object will bring back sharpness - it won't.

I think there is a good chance that on my camera the center focus point is three times more sensitive than any of the other eight points, and it is this one that is most accurate. But so is the case with many cameras, with the exception of high-tech new models like the Canon 1Ds Mark III or Nikon D3X. Other possible the reason is that most lenses are sharpest in the center and lose sharpness towards the edges.

Here are three of the most typical examples of what I shot on two different cameras. An insert is an inscription on a scale of 100%.

Center focus point, no composition change. Lens 50mmf 1.8.

Lens 50mmf1.8. Central focus point. The camera is moved to the left after fixing the focus.

Lens 50mm f 1.8. Left focus point. Focus on the object.

What can I say - whether to switch the focus point or not, in my opinion, is a matter of time. But try it yourself, your result may differ.

A small note on macro - such shots should always be taken with a tripod and manual focusing, due to the extremely shallow depth of field and the proximity of the lens to the subject.

7. Use the correct focus mode

Most DSLR cameras have at least two similar focus modes. The first is "One Shot" (Canon) or "Single Servo" (Nikon). This mode assumes that the object is stationary. Focus locks, you get lighting confirmation on the internal display, and then you release the shutter. You will not be able to release the shutter if the focus is not locked.

The second type is “AI Servo” (Canon) and “Continuous Servo” (Nikon). This mode is suitable for shooting subjects in motion, including sports, wildlife, etc. The camera finds the subject using the focus point, and the focus will constantly change to keep up with the subject, but will never lock. The shutter button will work even if the focus is not perfect.

There are also other modes on some cameras, such as Canon's AI Focus, which are great when the subject is static but may start to move, as is the case with young children. Autofocus will lock on the subject, but if the subject moves, the camera will enter AI Servo mode to track it.

The third option, pre-focus, is for objects that are moving towards or away from you. The camera will try to predict the movement and give you an acceptable focus.

8. Don't change depth of field for good focus

Although using a larger depth of field with a smaller aperture can increase the "apparent" sharpness of an image, remember one thing: no matter what the depth of field is, there is only one point of focus. So always practice good focusing techniques no matter what depth of field you use.

9. Use a tripod or find a foothold

When we take a photo, we all unconsciously sway back and forth - in particular, leaning towards the subject with a heavy camera and lens kit. It `s naturally. Everyone has it to one degree or another. And if you're shooting with a very shallow depth of field, that small amount of distance you shift can have a big impact on the sharpness and the sharpness of focus you want. If you're using a 4" depth of field, a 2" offset can have a disastrous effect. So use a tripod.

Now I have to add, since I use a tripod myself - I hate them. They affect the way I work and, most of the time, the way I shoot. So, if you'd rather avoid using a tripod, at least take the time to practice being a good photographer. One foot in front of the other, legs slightly bent, arms at sides, not dangling in space (remote controls can be useful here), and body weight distributed centrally over the legs.

10. If still unsuccessful - use manual focus

I hear a deep sigh every time I offer this to photographers. They regularly state, "I shoot only in manual mode, never on automatic." But offer them one more time manual focus, and they will look at you as if you just offered them to sell their children. Manual focus in most cases (given that your diopters are set correctly) will achieve the best and most accurate result. Especially in this digital age, when it's so easy to see an image at 100% or even 200% magnification on our monitors.

In fact, if you look at the unofficial autofocus specs, you'll notice that they aren't very accurate. Here is the specification for "sharpness": An image is considered sharp if it appears sharp in print 6x9 from a distance of 10 inches. Yep, that's it. No 100% zooms, no 20x30 prints. Just this.

Today, a number of new cameras are being produced with a built-in Live View mode. This can be a useful tool for manual focusing. Turn on your Live View, zoom in on the subject/focus point and check the sharpness on the display. This doesn't work very well in my case, as I'm almost always in bright environments: deserts, beaches, etc. - but for some it will work just fine.

One note about the image above. I usually use it to show the manual focus switch, but the other switch is also of interest: "1.2m to infinity" and "3m to infinity". This switch is related to what I was talking about earlier: don't make your lens hunt for focus through as much space as possible. If you know you won't be focusing on anything closer than three meters, move the lever to the appropriate position and the lens won't have to wander around looking for focus. This can result in more accurate primary auto focus.

11. What should I focus on?

For close-up portraits, the consensus is, in general, worked out: the eyes. For other types of portraits, it's still the face, unless you intentionally want to focus on some other part of the body. Focus precisely where you want the viewer's eye to go.

Landscapes aren't always easy, but you still need to stick to the rule mentioned above. Do not bet on the fact that "this is a landscape with a wide viewing angle, focus on infinity." If you have a subject in the foreground, focus on it and let your depth of field bring the image into the background. If the object in the foreground is not in sharp focus, it is confusing, because in natural conditions we usually see objects that are closer rather than distant ones.

I can now work with focusing at "Hyper Focal Distance", but that's out of the scope of this tutorial. If you are interested in this topic, which is likely, use a quick Google search.

12. Is the subject in focus, but is it sharp?

Focus and sharpness are two different things. Explaining the concept of sharpness can take another lesson of its own, so I'll just point out a few useful points.

If an image is out of focus, you cannot bring it back into focus by sharpening it. You will only get a very sharp out-of-focus picture. Most RAW images need some sort of sharpening. Whether you're using Smart Sharpen, Un-sharp masking, or high pass filtering techniques, most RAW images benefit from sharpness. However, as I gradually started using higher and higher quality cameras, I saw less and less need for sharpening, and now I only use this tool in about 25% of my frames.

Remember also that sharpness depends on the final product. You won't sharpen in the same way on an image that goes to the web as you would on a 16x20 print. And with that in mind, if you intend to sell your photo through a stock agency, don't sharpen it at all. Most will tell you not to do this because you can't predict what the image will be used for and at what size.

On the left are images directly from the camera, unedited ("Straight Out of the Camera"), on the right - with added sharpness.

13. Consider exposure

Shutter speed is another setting that can lead to a lack of sharpness. Each person has a limit on the shutter speed at which he can shoot handheld on lenses with different focal lengths. Some people are more stable than others, but if you're shooting at a shutter speed that can't compensate for the movement (trembling) of your hands, your image will come out blurry. When it comes to standard and wide angle lenses, most people can shoot handheld with them consistently at around 1/30-1/60 of a second.

Larger telephoto lenses require much faster shutter speeds. The general rule people start with is "1 to the focal length of the lens". So, if you have a 200mm lens, shoot at 1/200th of a second, and start from that level to understand your further possibilities. Personally, I'm shaking like California on its worst days, so I usually shoot at faster shutter speeds. It also depends on how far away you are from your subject, as the farther you are, the more noticeable the movement.

If the subject is moving, keeping the camera stable or on a tripod won't help - you'll still need to choose a satisfactory shutter speed in order to stop the action. Most start at 1/250, but it depends on how fast the object is moving. The requirements also vary depending on whether you are shooting in a static position or following the subject. If the latter, you can choose a slower shutter speed and also get some cool effects. This will allow you to show movement in the background, but will freeze the object itself.

Image stabilization systems on lenses allow you to shoot handheld at faster shutter speeds (up to 3 stops), but will not "stop" movement any better than a lens without an image stabilization system. You can only capture the action with a shutter speed (or high-speed flash).

Image not out of focus. The shutter speed is too long.

14. Choose the right exposure

Correct exposure and good lighting (the essence of all photography) is the key to good focus and sharpness. While sharpness is determined by the line of contrast, if you underexposed the frame or shot in dim light, the image will not be sharp even if all other parameters of good focus are met.

15. I did it all. I'm still out of focus!

There is a small chance that something is really wrong with your hardware. Third-party lenses are sometimes not very well designed, and therefore will not always work perfectly with branded cameras. Some work great, others don't. But sometimes even branded lenses are not made perfectly.

Cameras such as the Canon 50D and 1D/Ds Mark III have excellent front and back focus adjustments for over 20 different lenses, so if you know one lens is perfectly focused in front of your subject all the time, you can adjust the camera. to fix it. If this option is not available, you need to determine if your lens, or both lens and camera, needs repair.

Here's a test you can do at home to see if it's you or the camera. Find a ruler and place it on the table away from the camera. Put the camera on a tripod and open the aperture as wide as possible. Take a picture of the ruler at a 45-degree angle, focusing on a specific mark - in this example, the six.

If this is the mark that you will see as clearly as possible when you open the image, then everything is in order with your equipment - get back to working on your technique! If the sharpest point is before or after this mark, then you will know that this is a hardware problem and should be taken to service.

16. Conclusion

I covered a lot of questions in this tutorial - great that you read to the end! It seems to me that good focus and sharpness are two of the most important technical parameters that must be preserved in an image. This can make a difference between shots that look professional and those that look like amateur work (and we all want to look like professionals - whether we are or not).

Please feel free to leave your opinion in the comments - have you ever had problems with focus and sharpness?

Article text updated: 06/28/2019

Many modern SLR cameras are equipped with such advanced autofocus systems that it is often difficult to figure out how to use them. Whether we shoot with an entry-level camera or a professional camera, to get sharp pictures, we need to try to figure out how to use the different autofocus modes. Incorrect focusing, a blurred image can destroy the positive impression of the picture, and it is impossible to correct this shortcoming during post-processing in a graphics editor. Some photographers convert their photos to black and white to hide focus issues. If we learn how to focus correctly, we don't have to resort to these kinds of tricks, we get a much better result that our viewers will love. A clear image is what people want to see today when looking at our pictures. Someone may argue that sometimes a fuzzy picture looks “creative”, but here you need to understand: it’s one thing when we smear a photo for a specific purpose, and another when we spoil the picture because we don’t understand the work of our camera’s focusing system. Once we understand how DSLR autofocus works, we can decide for ourselves when and to what extent the image will be out of focus.

Photo 1. Lessons for beginners. To get a high-quality photo, you need not only to choose the correct shutter speed, autofocus mode, but also be able to quickly rotate the zoom ... Nikon D610 camera. Nikkor 70-300 telephoto lens. Settings: ISO 1000, FR-98mm, f/5.0, V=1/2500 second

In today's free photography tutorial, we'll cover the basics of autofocus modes on DSLRs. Since the operation of automatic focus directly depends on what type of camera and its model we use, we, of course, will not describe in detail absolutely all AF modes, but will analyze a couple or two examples for clarity. Since I myself now have a full-frame Nikon D610 camera, and before there was a cropped Nikon D5100 camera, more emphasis will be placed on the work of this manufacturer's DSLRs. Well, I beg your pardon for absolutely beginner amateur photographers for the fact that the photo lesson will use specific vocabulary that is more understandable for advanced photographers.

1. How the autofocus system of SLR cameras works

One of the nice things about modern cameras compared to their film counterparts fifteen years ago is that we no longer have to manually adjust the focus. Digital photography is much more friendly to the amateur photographer in this aspect, because, unlike film photography, we immediately see the result and can easily change settings, retake a photo without thinking about the cost of film and photo paper. Over the past ten years, autofocus systems have become much better and even entry-level DSLRs boast a good autofocus complex. Well, how does such a system work in modern SLR cameras? Let's start with the very basics.

1.1 Active vs passive autofocus

There are two types of autofocus (AF) system: active and passive. Active AF “Active AF” functions by sending an infrared beam at our subject and picking up its reflection (“sounder” principle). The camera makes calculations and understands how far the object is from it, signals to the lens how much to adjust the focus. A nice advantage of the active focusing system is that it can work in very low light conditions, in which normal (passive) autofocus will fail. The disadvantage of “Active AF” is that this mode can only be used in stationary conditions, for shooting motionless subjects, and works only at short distances: up to 5-6 meters. If we take pictures with a Nikon or Canon flash that has an “AF Assist” autofocus function, it will work in active autofocus mode.

The “Passive AF” autofocus system is based on a completely different principle: it does not send an IR beam and does not pick up its reflection in order to understand how far between the camera and the focus object. Instead, special sensors inside the chamber are used to contrast definitions part of the light passing through the lens (called the “phase method”), or the camera matrix itself serves as such a sensor that determines the contrast of the image (called the “contrast method”).

What is meant by "defining contrast"? Without going into the wilds of terminology, this is the definition of sharpness in a certain area of ​​\u200b\u200bthe image. If it is not sharp, then the autofocus system adjusts the lens until sharpness / contrast is achieved.

This is why the passive autofocus system needs enough contrast in the frame to function properly. When the lens starts to “scrawl” over a uniform surface (such as a white wall or some kind of smooth tonal surface), this is because the camera needs objects with edges (contrast) that separate from the background in order to understand how adjust focus.

By the way, if there is an AF assist lamp on the front panel of our DSLR, this does not mean that the camera is in active focus mode: all that the lamp does is illuminate our object like a flashlight, i.e. The camera is operating in “passive AF”.

Many digital cameras, such as point-and-shoot cameras, camcorders, and the like, most often use a "contrast AF method" to achieve focus. At the same time, most modern DSLRs can be equipped with both systems for focus correction: phase and contrast autofocus.

Since the “contrast method” requires light to hit the sensor, the SLR camera must have the mirror up when focus is determined, which means that contrast autofocus in a DSLR can only be performed in “Live View” mode.

The phase method is great for focusing on moving objects, and the contrast method is great for stationary ones. Contrast-detect autofocus often performs better than phase-detection AF, especially in low light conditions. The advantage of contrast focusing is that it is enough to use any part of the image (including the one at the very edge) on the matrix to adjust the sharpness, while phase focusing requires the use of one or more focus points of the SLR. The disadvantage of the contrast method today is that it is relatively slow.

Many professionals believe that camera manufacturers will be able to solve this problem in the foreseeable future, as the speed of autofocus when shooting video is becoming more and more important for DSLRs, and some mirrorless cameras (in particular, the Micro Four Thirds, 4/3 standard) are already equipped with fast contrast AF. Modern high-end mirrorless cameras have two autofocus systems: a fast phase-detection autofocus for working in good light and a slow contrast autofocus for low-light conditions. Some manufacturers, in general, managed to embed the pixels of phase sensors directly into the camera matrix, which, in comparison with the traditional phase autofocus system of DSLRs, greatly increased the accuracy of the system.

If everything above sounds confusing, don't get too upset: the technical information presented above is intended to provide a general understanding of how autofocus works in a camera. Just remember that focus errors in the camera happen due to the lack of light passing through the lens and the type of focus mode we have chosen (as explained below).

1.2 Focus points

Focus points are small empty rectangles or circles that we can find in our camera's viewfinder. Manufacturers often differentiate between amateur and professional cameras by building different autofocus systems into them. Entry-level DSLRs typically have a minimum number of focus points to focus on, while advanced DSLRs come with a complex, highly configurable AF system with a large number of focus points. They are part of the "Phase AF Method" so that each point can be used by the camera's AF sensor to determine contrast.

Focus points are deliberately located in a certain part of the frame, and their number differs not only from different manufacturers, but also from different models of cameras. Here is an example of two different types of autofocus with a different number of focus points and their arrangement.

As you can see, the Nikon D5100 DSLR has 11 points, while the Nikon D810 has 51 of them - a big difference in the number of sensors. Does the number of focus points matter? Certainly - yes! This is not only because it is easier for us to compose a particular shot by focusing on a specific area of ​​the image, but also because the AF system can more effectively track the subject in the frame (extraordinarily handy when shooting sports and wildlife). Although, it must be borne in mind that not only the number of focus points in our camera matters, but also their type.

1.3 Types of points in the DSLR AF system

Let's talk about the different types of autofocus points in DSLRs. As stated above, the number of points is not the only important parameter of an autofocus system. The type of points is also critical to achieving accuracy. There are three types of focus points: vertical, horizontal and cross. Vertical and horizontal work in the same direction, i.e. these are linear sensors. Cross dots measure contrast in two directions, making them more accurate. Therefore, the more cross sensors in our DSLR, the more accurate the AF system works.

That's why, when a new model of a SLR camera is announced, in the review we can read something like: "The number of focus points is X, of which Y is a cross type." The manufacturer proudly emphasizes the number of points, especially the presence of cross points, if there are more of them in a new camera. Here, for example, in the list of the main differences between the Nikon D7200 and Nikon D7100 from the earlier model Nikon D7000, it was indicated that they have 51 focus points, including 15 cross points, and the old woman has 39 points, cross points - 9 pieces.

When we buy a new SLR camera that we plan to use for shooting sports or for hunting, we need to pay close attention to both of these parameters.

1.4 Other factors affecting the efficiency of the camera's autofocus system

As we can see, both the number of focus points and their type are important. Although, not only they affect the operation of auto focus. The quality and quantity of light is another parameter that greatly determines the performance of autofocus. Every photographer has probably noticed that the camera focuses perfectly when shooting on a bright sunny day on the street, and as soon as we enter a dimly lit room, the lens starts to “scour”. Why is this happening? Because, in low-light conditions on the subject, it is much more difficult for the camera to measure the differences in the contrast of the scene. Remember that passive autofocus is completely dependent on the light passing through the lens, and if the quality of the lighting is poor, then autofocus does not work satisfactorily.

Speaking about the quality of light, we should not forget about the features of the lens, that the maximum open aperture also has an effect on AF. If we shoot with old glass that has mold, dirt, too much dust, or there are problems with front and back focus, then auto focus, of course, will not work very accurately.

This is why professional lenses at f/2.8 allow you to focus much faster than amateur lenses at f/5.6. The f/2.8 aperture is the most suitable for fast focusing: the aperture is not too wide, not too narrow. By the way, usually lenses at aperture 1.4 focus more slowly than at f / 2.8, since more rotation of the glass elements inside the structure is required to correctly focus .

Focusing accuracy is important at these wide apertures because the depth of field is very small. Ideally, the aperture should be between f/2.0 and f/2.8 for the autofocus system to function at its best.

Smaller apertures, such as f/5.6, will cause less light to pass through the lens and make it harder for the autofocus system to work. For this reason, open apertures (with the exception of f/1.4) are preferable to clamped ones.

It should also be added that all modern digital cameras focus at an open aperture, so no matter what aperture value we choose (for example, f / 22), the aperture changes only at the moment of shooting .

Finally, the overall quality and safety margin of the autofocus system is of the highest importance. For example, the top professional Canon 1D Mark III DSLR, designed for shooting sports and hunting, after being released into the series, spoiled its reputation due to problems with autofocus. And it took forever for Kenon to release firmware to fix these shortcomings that annoyed professional photographers. Many of them switched to Nikon cameras precisely because of focusing problems. The camera was equipped with all autofocus modes, but it did not work correctly under certain conditions.

If we want the best autofocus system in today's DSLRs, especially for sports and wildlife photography, Nikon or Canon should be the choice (although other manufacturers are quickly catching up with the market leaders).

2. Autofocus modes of digital DSLRs

Most DSLRs these days have the ability to shoot in a variety of out-of-focus modes depending on the situation.

It is one thing when we photograph a portrait of a calmly sitting person, and another when we shoot a running athlete or a flying hawk. When we shoot a stationary object, we focus once and take a photo. But in case the subject is in continuous motion, we need the camera to automatically adjust the focus at the moment when we take the picture. The good news is that our camera has a built-in function to work effectively in this situation. Let's look at each of the focus modes in more detail.

2.1 One-Shot Focus Mode

Single-frame tracking focusing in Nikon cameras is designated “AF-S”, in Canon cameras this type is called “One-shot AF”. And it is an easy way to bring the lens into focus directly. We choose a focus point, and the camera measures the contrast simply by one point.

If we press the shutter button or the assigned AF button (if this assignment is possible in our model) halfway, the camera focuses, but if the subject moves, it does not refocus, even if we continue to keep the shutter button pressed halfway. That is, the focus remains "locked".

Normally, in single-servo AF mode, the camera must first focus in order for the shutter to be released. Therefore, if focus fails or the subject moves, pressing the shutter button will do nothing (due to a focus error). In some camera models it is possible to change the camera's reaction to the lack of focus (for example, with Nikon D810 we can set the “AF-S Priority Selection” setting in the “Shutter” custom settings menu, which will allow us to take a picture even if the camera is not in focus) .

There are a few things to keep in mind about AF-S mode: if we have installed an external flash that has a red AF-assist beam, it will require the camera to be set to AF-S mode for it to work. The same is true for the auto focus assist lamp built into the front panel of the camera: it only works in AF-S mode.

2.2 AI Servo Focus Mode

Another focusing method available in modern DSLRs is called "Continuous Servo AF" or AF-C by Nikon and "AI Servo AF" by Canon. It is used to track moving subjects, and is essential when photographing sports, wildlife, and other non-stationary subjects. The principle of operation of this mode is based on analyzing the movements of objects and predicting where it will be in the next instant, and setting the focus to this point.

The advantage of this mode is that the focus is automatically re-adjusted if the photographer or subject moves. All that is needed is to continue to hold the shutter button (or the assigned key for AF, if there is an assignment option) in the half-pressed state. The autofocus system will automatically track the subject. Compared to AF-S single-servo focusing, AF-C continuous focusing is typically highly customizable (especially on the most expensive DSLRs) and can perform complex tasks such as tracking subjects to one or more focus points.

2.3 Hybrid One-Shot and Tracking Focus

Some cameras also have another mode called "Auto Servo AF" "AF-A" for Nikon or "AI Focus AF" for Canon cameras. It is a kind of hybrid, automatically switching between single-frame and continuous focusing. If the camera determines that the subject is still, it switches to AF-S, and if the subject is moving, it switches to AF-C.

In cheap DSLRs, AF-A mode is enabled by default and works decently enough in many situations. Many professional cameras do not have Auto Servo AF as it was designed for beginners.

2.4 Continuous focus tracking

Continuous focus focus mode, designated by Nikon with the letters “AF-F”, was introduced by the company for the new Nikon D3100 and D7000 models. It is intended mainly for shooting in Live View format. In this mode, the camera follows the subject and automatically adjusts the focus during video recording. Although the name sounds nice, in real life this mode does not work very well when shooting fast moving objects. Nikon Corporation engineers still have a lot of work to do to bring the “AF-F” mode to perfection. If you do not shoot video on a DSLR, then you should not turn on this mode.

Many professional photographers in photography lessons for beginners note that most of the time they have AF-C continuous focus tracking turned on, and only when the camera cannot focus in poor lighting conditions, they switch to AF-S.

2.5 Changing focus modes

If you do not know how to change the auto focus mode on your camera, it is better to read the instructions for it, as this happens differently for different models. For example, for entry-level cameras Nikon D5300 or Nikon D5200, you need to press the "Info" button and select the focus mode with the joystick. And expensive DSLRs have a special button on the front panel, with which you can quickly switch between different modes. Here, for example, is how to change the AF mode on the Nikon D610 camera: press the AF mode button and simultaneously turn the control wheel.

The letter “C” appeared on the auxiliary screen, which means the camera is working in AF-C continuous focusing mode, switched to “S” - frame-by-frame focus turned on. Press "M" - switched to manual control of the camera focus.

3. AF area modes

To confuse novice photographers even more, many SLR cameras have items in their menus called something like “AF area mode” that allow the amateur photographer to select several options for how focusing will work in AF-S, AF-C, AF- A and AF-F.

For entry-level DSLRs, such as Nikon D3100 or Nikon D5200, the settings can be changed through the menu, while for advanced cameras, such as Nikon D300s, Nikon D700, Nikon D3s or Nikon D3x, they are changed with a special selector on the rear panel (for SLR cameras, Nikon D810 and Nikon D4S cannot be reassigned to control this parameter to other buttons). Let's see what the AF area selection gives us.

3.1 Single point focusing area

When we select "Single Point AF" on a Nikon camera or "Manual AF Point" on a Canon camera, we only use one point to focus through the viewfinder to focus. That is, when we switch from one point to another with the joystick, the camera measures the contrast only in this particular section of the image, using vertical or cross sensors (depending on which one we have chosen). Many professional photographers advise using the single-point focus mode when shooting landscapes, architecture, and other stationary subjects.

3.2 Dynamic Focus Area Mode

In "Dynamic AF" mode for Nikon or "AF Point Expansion" for Canon cameras, we select one focus point, and the camera first adjusts focus on it. Further, once the focus is set, if the subject is moving, the camera will use the surrounding points to follow it and keep the focus on the subject. We expect it to follow the movement of the subject and keep it in focus while keeping the camera close to the initially selected focus point. If the camera selects surrounding/other points, it will not be visible in the viewfinder, but it will be noticeable in the finished photo.

Dynamic AF works great when shooting fast-moving subjects such as birds, because it's not easy for us to keep a bird in focus while it's flying. Advanced DSLRs, such as Nikon D7100, Nikon D7200 or Nikon D800, allow you to choose the number of dots surrounding the main one: 9, 21 or 51 pieces.

Thus, when we want to track a small area in the frame, we select 9 points, and if we need to track movement across the entire field of the frame, we assign 51 points.

Recently, many Nikon DSLR models also have a “3D tracking” mode - when we assign a point, and the camera then decides how many auxiliary ones it needs to track the change in the position of the object in the frame. The advantage of the 3D tracking mode is that the camera uses a built-in image recognition system, automatically reading colors and following the subject on its own, and you simply compose the picture while the subject is moving.

For example, we photograph a white heron pacing among black birds. System 3 Dtracking will automatically focus on a white bird and follow it even if the bird moves or the camera moves, allowing us to compose the shot .

If we compare the modes "Dynamic AF" and "3D Tracking", then in the first case a certain number of points will be used, and in the second - all available to follow the subject. In this case, "Dynamic AF" uses certain "zones", activating only the surrounding focus points (as many as we have selected in the settings). For example, we have selected 9 points, tracking will work as long as the object is in the zone of 9 focus points surrounding the main one. If the subject leaves this area, the camera will not be able to focus. But in the 3D tracking mode, the camera will continue to observe the object (the newly selected points will be displayed in the viewfinder), even if it is significantly farther away from the originally selected point.

Professionals use the dynamic autofocus mode during bird and wildlife photography, using a small number of points: 9 or 21 pieces. There are different opinions about 3D tracking, as it is not as fast as with, for example, 9 dynamic AF points.

3.3 Auto focus area selection mode

For Nikon cameras, it is referred to as "Automatic AF area selection", for Canon - "Automatic AF Point Selection" and is a point and shoot method of focusing. The camera automatically chooses what to focus on. This is a complex system that can recognize the color of a person's skin in the frame and automatically focus on it. If there are several people in the frame, the focus will be selected on the one closest to the camera. If there are no people in the frame, then, usually, the camera focuses on a near or far object. If we have selected AF-S and Auto-area AF modes, the viewfinder will display the engaged focus point for a second, allowing us to confirm the area the camera has focused on.

The same is possible with Canon cameras, but they have this mode called “Automatic AF point selection in One-Shot AF mode”. It's hard to say why this mode is needed, because professionals like to control all the shooting parameters, instead of letting the camera do it for them.

3.4 Group focus area mode

The latest Nikon SLR cameras, such as the Nikon D810 and Nikon D4S, have a new focus area selection mode “Group AF”. Unlike "Single-point AF", not one, but five focus points are used to track subjects. This mode is better for setting the starting point for focusing and tracking subjects than "Single-point AF" or "Dynamic AF", especially when it comes to shooting small birds that constantly flutter from branch to branch and can be difficult to catch in focus and follow them. In such cases, “Group AF” can be of great help to the photographer and produce better results than “Dynamic AF” because it is more accurate and gives shot-to-shot stability.

How does the group focus area mode work? We see 4 focus points in the viewfinder, the fifth, in the center, is hidden. We can move the group by pressing the joystick on the back of the camera (ideally we want to stay in the center because the focus point in the middle of the frame is a cross point, more accurate). When we have aimed at the subject, all five points are activated at the same time for initial focusing with priority on the nearest subject.

This is different from "Dynamic AF" with 9 points, which has priority on the selected center point. If it was not possible to focus on the central one (low contrast), the camera will try the remaining 8 pieces. Initially, the camera always focuses on the center point, and only then moves on to the other 8 pieces.

In turn, “Group AF” uses all 5 points at the same time and tries to focus on the nearest subject without giving the advantages of any of the 5 points.

Group AF mode “Group AF” is especially useful for shooting birds, wildlife, and non-team sports. In the cyclist example above, if our goal is to focus on the athlete in front, Group AF would be a better choice, as this mode will keep the camera following the athlete closest to it.

Another good example is a bird sitting slightly above the photographer so that the background behind it is almost invisible. In Dynamic AF mode, no matter where you aim, the camera will first try to focus. If we aim the lens directly at the bird, the camera will focus on it. If we accidentally aim at the background, the camera will focus on it.

Therefore, shooting small birds can be a little difficult, especially in bushes, or if the branches on which they sit are constantly staggering. The choice of the initial focus point is very important, and the sooner we choose it, the higher the chances of catching the bird in focus and following it, especially if it suddenly decides to fly away. As stated above, the “Group AF” mode does not benefit from any focus point, all 5 pieces are activated at the same time. In this case, since the bird is sitting closer than the background, once the group of 5 points is close to it, the camera will always focus on the bird and not the background. Once we have selected focus, the camera in Group AF will follow the subject, but again only if one of the 5 points is next to the subject. If the subject is moving fast and we don't have time to turn the camera in the same direction, the focus will be lost, just as it would be with 9-point Dynamic AF.

Some photographers say that the "Group AF" mode allows you to capture focus quite quickly, but no one really measured whether it is faster than 9-point dynamic focusing. Perhaps the latter in some situations will be faster.

Another important fact to pay attention to is that when we turn on the group auto focus mode when focusing single frame AF— S, the camera turns on the face detection function and tries to focus on the eyes of the person closest to it who stands out from the group. For example, if we are photographing someone standing between the branches of a tree and foliage, the camera will always try to focus on the subject's face, instead of focusing on the leaves. .

Unfortunately, face detection is only possible in AF-S mode, so if we are photographing a group of fast moving athletes and we need the camera to lock focus and follow the faces of the subjects (rather than focusing on nearby objects), we are better off using the Dynamic mode. AF" for Nikon or "AF Point Expansion" for Canon cameras.

Here is a schematic comparison of each of the auto focus modes for Nikon cameras.

When viewing images clockwise: Single-point AF, Auto-area AF (9, 21, and 51), 3D Tracking, and Group AF.

3.5 Other focus area selection modes

Latest DSLRs have new area selection modes such as Face Priority AF, Wide Area AF, Normal Area AF, and Subject Tracking AF. These modes are used when shooting video on a SLR camera. Most likely, these functions will be built into the entire line of Nikon DSLRs capable of shooting video. We will not discuss these modes in detail, since their functioning in different cameras is slightly different and may be changed in the future.

Canon also has its own AF area selection modes such as “Spot AF” where we can fine-tune focus within the focus point. This mode is highly specialized, it can be found, for example, in Canon EOS 7D cameras.

3.6 When to choose one or another type of auto focus

Why do we need to know how and when to use the different AF area selection modes? Because each of them can be combined with the focus mode! To better understand this, let's make a table with examples (for Nikon SLR cameras).

Note to the table of explanations of the focus area selection modes above: certain options may not be available in different models.

3.7 Changing focus area selection modes

To understand how to change the focus area selection mode on your camera, it is better to read the instructions. For entry level DSLRs like Nikon D3100 or Nikon D3300, you need to enter the “Shooting Menu” section, and advanced cameras have a switch on the back. Here, for example, is what the auxiliary display looks like on Nikon D600 and D610 SLR cameras.

We press the AF button at the base of the mount, and without releasing it, rotate the front and rear control wheels.

4. Autofocus scenarios and examples

Well, we learned a lot of technical information about what each of the auto focus and AF area selection modes are. Let's go through more scenarios and look at examples to better understand and assimilate the data presented earlier. The camera settings described below are taken from Nikon cameras.

4.1 Scenario #1 - Filming outdoor sports

What autofocus mode and type of AF area metering will we choose when photographing, for example, football? Let's start by choosing the right focus mode. Obviously, single-servo AF-S won't work, as we want the camera to focus continuously as long as the shutter button is half-pressed (well, or whatever button we assigned to AF). Therefore, we must use either AF-C or AF-A mode. Professionals want to take full control of the shooting process, so they switch to AF-C continuous-servo autofocus in such a situation.

What about AF area selection? Should we enable Single-point AF, Dynamic AF, Group AF, or 3D Tracking? Professional photographers shooting sports like football, basketball or outdoor hockey will turn on 3D tracking, allowing the camera to watch the athletes while the person is composing the shot. If it suddenly turns out that 3D tracking does not work correctly, it often makes mistakes, then you can switch to "Dynamic AF" with a fairly large number of focus points, especially if we are standing close to the scene. Group AF will only work well if we are standing very close to the subject. Here is a set of focus mode settings for the described cases:

1. Auto focus method: AF-C
2. AF area metering mode: 3D Tracking, Dynamic or Group AF
3. Custom Settings => Dynamic AF: 21 or 51 points
4. Custom Settings => AF-C Priority Selection: focus priority

4.2 Scenario #2 - Shooting people on the street

When we photograph people posing for us in nature on a sunny day, any of the focus modes should work well. If we chose AF-S, the camera will focus once as soon as we half-press Shutter, so we just need to make sure our subject doesn't move after focusing. By default, the camera will not allow you to take a photo in single-servo AF-S mode if the focus is not achieved.

If, however, we shoot in AF-C continuous focus mode, then we just need to make sure that the focus is correct before pressing the button. Also, AF-A is good for shooting portraits.

As for selecting the AF metering area, it is more convenient to shoot with "Single-point AF" because the subject is stationary.

1. Modeautofocus: AF-S, AF-C or AF-A
2. AF metering area: single point
3. User settings => Priority selection for AF-S: focus priority
4. Custom Settings => AF-C Priority Selection: release priority

Probably not worth mentioning that we should always focus on the nearest eye of our model, especially if she is close to us.

4.3 Scenario #3 – Shooting portraits indoors

Photographing people inside a building in poor lighting can be a little tricky. If the room is dark, you can switch to AF-S single-servo focus mode so that the assist lamp will help us if necessary. If we have an external flash, the AF-S mode will turn on the red beam to adjust the focus.

In AF-C mode, this function cannot be used. And the AF-A autofocus should do the job, too, but professional photographers will prefer to turn on AF-S.

As for AF area metering, it is more convenient to use the center focus point for greater accuracy in low light conditions.

1. Autofocus mode: AF-S
2. Measurement: Single point AF
3. User settings => Priority selection for AF-S: focus priority

4.4 Scenario number 4 - photographing birds on the fly

Shooting birds is an extremely difficult genre of photography because it is difficult for us to predict their behavior and they often fly very fast. As noted above, when hunting it is better to select the Continuous Tracking AF (AF-C) mode, and the focus area is either Group AF or Dynamic AF from the 9th or 21st (I would like to take pictures at 21 points , but usually 9 pieces is faster). Professional photographers say they've tried 51 focus points and 3D tracking, but these modes are slower and less accurate than with fewer points.

One of the photographers told me that in 99% of cases he focuses on the birds on the central point, changing it only when the birds are sitting high on some branch. Once again, the central focus point will give the best result in most cases. If we are shooting small birds and there is no time to set the initial focus point, we can try the Group AF mode (if available on your camera).

1. Autofocus mode: AF-C
2. AF area metering: Dynamic or Group AF
3. Custom Settings => Dynamic AF: 9 or 21 points
4. Custom Settings => AF-C Priority Selection: release priority

4.5 Scenario #5 – Shooting landscapes and architecture

For these types of shooting, all focus modes are suitable, but it is more convenient to use AF-S, since we do not have objects to follow.

In poor lighting conditions, we will not be able to use the AF-assist illuminator function, because the distances are very long. In this case, you can mount the camera on a tripod and switch to Live View in order to focus on the bright object of our scene with a contrast method. If this does not help, one thing remains: turn off auto focus and focus manually.

When shooting landscape or architectural objects, we need to be more attentive to what our camera is focused on and remember that the need for a clear understanding of what depth of field (DOF) and hyperfocal distance is of particular importance.

One thing can be said about the AF area metering: we definitely need the “Single-point AF” mode to focus exactly on a specific point in our frame.

1. Autofocus mode: AF-S
2. AF area selection method: Single point AF
3. User settings => Priority selection for AF-S: focus priority

4.6 Scenario #6 – Shooting Large Animals

On a photo safari, when shooting large animals, professionals prefer to use the continuous AF-C tracking mode and the AF area metering method "Dynamic AF" or "3D tracking", both of which work perfectly. Animals are usually not as nimble as birds (although sometimes they can move even faster), so if we're not shooting fast action, it's better to use Dynamic AF with more focus points or apply 3D tracking.

1. Auto focus mode: AF-C
2. AF area selection: dynamic focus or 3D tracking
3. Custom Settings => Dynamic AF: maximum number of points or 3D
4. Custom Settings => AF-C Priority Selection: release priority

Hopefully, the scenarios listed above will make it easier to understand when and how to choose one or another focus mode and focus area metering. Now it's time to return to the table above and check if we understood everything well.

4.7 Scenario #7 – Photographing small groups

Beginners often ask what mode to focus on when we shoot a group of several people. Before talking about autofocus mode, there are some important things to discuss. If we are using a standard focal length lens or a wide aperture telephoto lens, we need to keep in mind the distance to the subject. When we stand close to our group and shoot at f/1.4-f/2.8, it can happen that only a couple of people are in focus, and the rest are blurred, unless they are standing in the same plane. There are two solutions here: either stop the aperture to f / 5.6 or f / 8, or move further away to increase the depth of field. Or you can use both of these tips.

If we want to blur the background and shoot at a large aperture, we can only put everyone in a row, strictly parallel to the camera. Imagine how it would be necessary for people to stand if they pressed their heads against a flat wall - this is how our models should be positioned.

As for the focus modes, in the daytime they will all work well, but it is more convenient to use a single point focus.

1. Modesautofocus: AF-S, AF-C or AF-A
2. Measuring method: Single point AF
3. User settings => Priority selection for AF-S: focus priority
4. Custom Settings => AF-C Priority Selection: release priority

Note: As you can see, in all modes, the priority selection for “AF-S” and “AF-C” is set to “focus priority” and “release”, respectively. And that's why. By setting the single-servo focusing mode to AF-S and “focus priority”, we tell the camera not to let it take a picture if it could not focus. Professional photographers don't use AF-S very often, but when they do, they want the shot to be sharp.

For AF-C continuous-servo autofocus, "release-priority" works great in most situations: the camera adjusts focus as closely as possible, but doesn't allow too long shutter lags, allowing the photographer to shoot when they want to. It makes no sense to think for the AF-C mode about what priority to set: release or focus. In "release priority" the camera doesn't care about good focus or bad (why autofocus then?), and in "focus priority" it won't let you take a good picture until the focus is locked. If we need the focus to be this precise, we switch to AF— Sthen. Just set this parameter as shown in the examples above and forget about them forever .

5. Tips for improving autofocus performance in low light

As noted earlier, in good, sunny shooting conditions, the cameras do an excellent job of autofocusing. But when photographers start shooting in low light, they face a lot of problems, especially when shooting indoors. Here are some tips to make the autofocus system work better when there is not enough light:

1. Using the center focus point. No matter how many focus points our camera has 9 or 51, we still focus on the center, and not on the extreme ones, if we shoot in bad light, because it works more accurately. There is usually a cross sensor in the center, which works better than any other points in our camera.

But then what to do with framing and composition if we have to focus on the center point? The solution seems to be to reassign the autofocus function from the "shutter" button on the camera to another one located on the back of the camera. Then you can focus on the subject and recompose the frame. Most DSLRs, including entry-level ones for beginners, allow you to do this. Professional DSLRs have a button (usually called “AF-On”) that can be enabled through the menu by selecting “AF-ON Only” in the autofocus activation settings. But we have to be careful after recomposing the frame, especially when shooting with a small depth of field at an open aperture. When we focus and then move the camera, the focus will definitely shift, and we need to be careful to keep our subject sharp.

2. Turn on the autofocus assist light function on the camera or on an external flash. Whenever you have to shoot in low light, this feature helps photographers. To activate it, you need to make sure that the AF-assist illuminator is turned on in the menu and the focus mode is set to Single-servo focus - AF-S.

3. Selecting contrasting objects and faces. Instead of trying to focus on a flat, monochrome surface, look for "contrasting" objects that stand out from the background.

4. Add some light or turn on lamps. Sounds simple, but if we're having trouble focusing, what could be easier than adding a little more light or turning on more lights in the room? One professional photographer told how he had to shoot dances at a party. There was so little light that I had to shine a flashlight on the models to focus. Then he approached the organizer and asked to turn on the general lighting in the hall - all the problems were solved by themselves, and he was able to take great photos.

5. Keeping track of shutter speed. We may think that we have problems with focusing, but we should not forget that the shutter speed should be sufficient for handheld shooting. Details about the rule for determining the exposure time using the formula B=1/(2*FR) are described in a separate photo tutorial on DSLR settings.

6. Using a tripod. By using a tripod, we can achieve more precise focusing in poor light without having to worry about camera movement.

7. Let's use the contrast focus feature in Live View. With the camera on a tripod, we can try to focus in Live View mode, which, as we remember, can use a more accurate method of focusing on the contrast of objects in the frame. Many professional photographers find that whenever they have to shoot with a tripod, they try to use contrast focusing because it gives the best results. And, in general, it is more convenient to focus in Live View mode, since the image on the camera screen is larger than in the viewfinder.

8. Useful thing - a bright flashlight. If our camera model does not have a built-in autofocus assist lamp, we use a bright flashlight and ask someone to shine on our subject to try to focus. As soon as the sharpness is caught, we switch to manual focus mode and turn off the flashlight, take pictures “with self-timer”. I met the advice of professionals to use a laser pointer to focus when shooting night landscapes (do not forget that if you get into the eye of a person or animal, you can burn the retina).

9. Using manual focus. Such advice does not correspond to the title of the article, but we must be able to manually focus and not be afraid to do this. Sometimes manual focusing will turn out even faster than in automatic mode. Many landscapes, macro shots, and architectural photographs are taken with manual focus.

Photo 13. Another landscape shot with manual focus. HDR of three frames. Camera Nikon D610. Lens - Samyang 14 / 2.8. Tripod Sirui T-2204X.

P.S. Dear friends, colleagues and guests of the site! If you think that the article can be useful to other photographers, I will be grateful if you share a link to it on social networks, on specialized forums, and publish it on your blog. Just ask to put an active link to the source! The wife spent the whole day to draw all these frames on the photographs ... It is impossible that her work was in vain. Thank you! Good luck, sharp photos to you.

The camera's autofocus system adjusts the lens to focus on the subject and can make the difference between a sharp shot and a missed opportunity. Despite the seeming obviousness of the task of "clearness at the focus point", the hidden work required for focusing, unfortunately, is far from simple. This chapter is designed to improve the quality of your shots by providing you with an understanding of how autofocus works, allowing you to get the most out of it and avoid its drawbacks.

Note: Autofocus (AF) works either using the contrast sensors in the camera ( passive AF), or by sending a signal to highlight or estimate the distance to the object ( active AF). Passive AF can be carried out by methods contrast or phase detector, but both methods rely on contrast to achieve accurate autofocus; therefore, from the point of view of this chapter, they are considered to be qualitatively identical. Unless otherwise noted, this chapter deals with passive autofocus. We will also look at the active AF assist beam method towards the end.

Concept: autofocus sensors

The camera's autofocus sensor(s) are located in different parts of the image's field of view and are the whole system behind achieving sharp focus. Each sensor measures relative focus by changes in contrast in the corresponding area of ​​the image, and the maximum contrast is considered to correspond to the maximum sharpness.

Focus change:		Blur	semi focus	sharpness
	400%	Sensor histogram

The basics of image contrast are covered in the chapter on image histograms.
Note: Many compact digital cameras use the image sensor itself as the contrast sensor (using a technique called contrast AF) and are optionally equipped with multiple discrete autofocus sensors (which are more common with phase-detection AF). The diagram above illustrates the contrast AF method; the phase detector method differs from it, but is also based on contrast as an autofocus criterion.

The focusing process generally works as follows:

1. The autofocus processor (AFP) slightly changes the focusing distance.
2. AFP reads the AF sensor and evaluates how and how much the focus has changed.
3. Using the information from the previous step, AFP adjusts the lens to the new focus distance.
4. AFP sequentially repeats the previous steps until a satisfactory focus is achieved.

The whole process usually takes a fraction of a second. In difficult cases, the camera may not reach satisfactory focus and will start repeating the above process, which means autofocus failure. This is a terrible case of "focus hunting" where the camera constantly zooms back and forth without achieving focus. However, this does not mean that focusing on the selected subject is impossible. The next section discusses cases and causes of autofocus failure.

Factors Affecting Autofocus

The subject can have a huge impact on autofocus success, often more so than differences between camera models, lenses, or focus settings. The three most important factors that affect autofocus are the amount of light, the contrast of the subject, and the movement of the camera or subject.

An example illustrating the quality of various focus points is shown on the left; hover over the image to see the advantages and disadvantages of each focus point.

Note that all of these factors are interrelated; in other words, autofocus is achievable even on a dimly lit subject, if it has a high contrast, and vice versa. This has important implications for your choice of autofocus point: choosing a focus point that is on a sharp edge or a pronounced texture will help you achieve the best autofocus, all other things being equal.

The example on the left compares favorably in that the best autofocus points coincide with the position of the subject. The next example is more problematic because autofocus works better on the background than on the subject. Hover over the image below to highlight areas of good and bad autofocus performance.

In the image on the right, when focusing on fast-moving light sources behind the subject, the subject itself may be out of focus if the depth of field is shallow (as is usually the case when shooting in low light conditions like those shown).

Otherwise, focusing on the external illumination of the subject would probably be the best approach, minus the fact that this illumination quickly changes location and intensity depending on the position of the moving light sources.

If it is not possible to focus the camera on the ambient light, a less contrast (but more static and fairly well lit) focus point can be chosen by the model's legs or leaves on the ground at the same distance as the model.

However, the choice described above is hampered by the fact that it often needs to be made within a fraction of a second. Additional specific AF techniques for still and moving subjects will be covered in the appropriate sections towards the end of this chapter.

Number and type of autofocus points

The stability and flexibility of autofocus is primarily a result of the number, position, and type of autofocus points that are available on a given camera model. High-end DSLRs have 45 autofocus points or more, while other cameras may even have as little as one center point. Two examples of AF sensor locations are shown below:

The examples on the left and right show Canon 1D MkII and Canon 50D/500D cameras, respectively.
For these cameras, autofocus is not possible at apertures smaller than f/8.0 and f/5.6.

Note: The sensor is called "vertical" only because it detects contrast.
along a vertical line. The irony is that such a sensor, as a consequence,
best detects horizontal lines.

For digital SLR cameras, the number and accuracy of AF points may also vary depending on the maximum aperture of the lens used, as shown above. This is an important factor when choosing a lens: even if you don't plan on using the lens' maximum aperture, it can still help the camera achieve better autofocus accuracy. Further, since the center AF sensor is almost always the most accurate, for off-center subjects it is often best to use that sensor first to focus (before recomposing).

Multiple AF sensors can work simultaneously for increased reliability, or individually for increased uniqueness, depending on the camera settings selected. Some cameras also have "Auto DOF", an option for group photos that ensures that all points in a focus cluster are within an acceptable degree of focus.

AF modes: tracking (AI SERVO) or one-time (ONE SHOT)

The most widely supported camera focus mode is Single, which is best for still images. This mode is prone to focusing errors for fast-moving subjects because it is not designed for movement, and it can also make it difficult for the viewfinder to track moving subjects. Single focusing requires focus to be reached before a picture can be taken.

Many cameras also support an autofocus mode that continuously adjusts the focusing distance for moving subjects. Canon cameras call this mode "AI Servo" and Nikon cameras call it "continuous" focusing. The tracking mode works on the basis of an assumption about the location of the object at the next moment of time based on the calculation of the object's speed based on previous focusing data. The camera then focuses to a predicted distance in advance to account for the rate of descent (the delay between pressing the shutter and the start of the exposure). This greatly increases the likelihood of correctly focusing on moving subjects.

Examples of maximum tracking speeds are shown for various Canon cameras below:

Values ​​are for ideal contrast and illumination when using a lens
Canon 300mm f/2.8 IS L.

The graph above can be used to approximate the capabilities of other cameras. Actual tracking speed limits also depend on how uneven the movement of the subject is, the contrast and illumination of the subject, the type of lens, and the number of autofocus sensors used for tracking. Also keep in mind that using focus tracking can significantly reduce your camera's battery life, so only use it when necessary.

AF assist beam

Many cameras are equipped with an AF assist beam, either visible or infrared, which is used in the active autofocus method. This can be very useful in situations where the subject is underlit or lacks contrast for autofocus, although using the assist beam has its disadvantages as autofocus is much slower in this case.

Most compact cameras use a built-in infrared light source for AF operation, while DSLRs often use a built-in or external flash to illuminate the subject. When using the auxiliary flash, it may be difficult to achieve autofocus if the subject moves noticeably between flashes. Therefore, the use of auxiliary illumination is recommended only for stationary objects.

In practice: capturing motion

Autofocus will almost always work best when shooting motion in tracking (AI servo) or continuous mode. Focusing performance can be greatly improved if the lens does not have to search over a wide range of focusing distances.

Perhaps the most versatile way to achieve this is pre-focus the camera on the area where you expect a moving object to appear. In the cyclist example, the prefocus can be done on the side of the road, since the cyclist will most likely appear close to it.

Some lenses for SLR cameras have a switch for the minimum focusing distance, setting it to the maximum possible distance (closer than which the subject will in no case be) will also increase efficiency.

Note, however, that in continuous autofocus mode, pictures can be taken even if precise focus has not yet been achieved.

In practice: portraits and other static shots

Still shots are best taken in single focus mode, which ensures that precise focus is obtained before the exposure begins. The usual focus point requirements regarding contrast and lighting apply here, but a little movement of the subject is also required.

For portraits, the eye is the best focus point because it is the standard and because it provides good contrast. Although the center autofocus sensor is usually the most sensitive, the most accurate focusing for off-center subjects is achieved using off-center focus points. If you use the center focus point to lock the focus (and then change the composition), the focus distance will always be somewhat less than the actual one, and this error increases as the subject gets closer. Accurate focus is especially important for portraits as they usually have a shallow depth of field.

Since the most commonly used autofocus sensors are vertical, it may be appropriate to worry about whether the contrast prevails at the focus point, vertical or horizontal. In low light conditions, sometimes autofocus can only be achieved by rotating the camera 90° for the duration of focusing.

In the example on the left, the steps are predominantly made up of horizontal lines. If you focus on the farthest of the front steps (calculated to obtain a hyperfocal distance), in order to avoid autofocus failure, you can orient the camera to the landscape position for the duration of focusing. After focusing, you can optionally rotate the camera to portrait position.

Note that this chapter deals with how focus, not on what focus. For more information on this subject, see the chapters on depth of field and hyperfocal distance.