Autofocus is one of the most useful advances in modern photography. Majority modern systems Video surveillance is impossible to imagine without autofocus. Learning to control this technology is one of the most important skills of any photographer.
What is autofocus?
A good place to start would be to answer another question. What is focus? In photography, this concept is central; it refers to an image with high clarity, originality, and 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 vision, poor focusing makes the world appear blurry. Luckily, unlike our eyes, the focus of a lens can be adjusted to get what you want sharp, but this is not easy or even always possible. This is where autofocus comes to the rescue.
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 focusing, and can be used to improve focusing 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 almost always has focus set by default. Simply put, no autofocus means no confidence in what you're doing.
Don't you find it strange that after buying a fancy DSLR, autofocus seems less flexible than on your phone? With smartphones, everything is simple, you press a button with your finger, you get a nice little picture, and everything that is in the frame can be seen extremely clearly. What a nice trick.
This is the viewfinder screen of the D3100, which has an 11-point autofocus system. More advanced cameras now work up to 61 autofocus points.
Looking at a DSLR, you think, what a hassle it is to be limited by the number of dots in the viewfinder! Without going into too much detail, let's just say that DSLRs use a different autofocus method than digital cameras and smartphones, which do not particularly need 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 focus Special attention autofocus system on digital DSLR cameras instead of smartphones (if you wanted to read about the iPhone, just 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 on the object we want?
Autofocus vs. Manual focus
First, we need to look at what mode is selected in the menu. Most modes belong to the so-called “auto scene modes”, where the camera settings change depending on the type of shooting you choose. Naturally, these modes require autofocus (there are, of course, exceptions, such as macro mode).
For example, a DSLR camera's main mode is autofocus. When you press the shutter button, you are signaling certain points on the viewfinder to be highlighted. These focus points are a reflection of how the camera sees the subject. If this is not what you were trying to shoot, then you are out of luck.
In order to independently control 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. Focus accuracy varies from model to model. But usually DSLRs are similar in this regard. "Manual" mode will help you if you want to have full control over your shooting.
Of course, you can do it differently, but most photographers stick to this method. To focus on the objects in the center, you must pay attention. 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 autofocus point will coincide with it, and the image will come out much clearer.
Step 2.
The point should be directly on your subject; press the shutter button halfway for what is called pre-focus. Once this is done, your camera's AF LOCK will clearly "see" what you want to shoot, what the focal length of the subject is, and remember this even if you move the camera.
Step 3.
We have decided on the focal length, now you have complete freedom in the frame. Usually still subjects are pretty boring to photograph, but once you're happy with the composition, press the shutter button all the way.
We use the center button on the autofocus to focus on the subject for the first time, then, after AF locking, we can freely create. This is called pre-focusing.
Select the focus point manually.
This very rare to ensure the focal point is exactly where you want it, even with the new 51-point systems. So if we have the ability to change the composition after pre-focusing, what's the point of additional points?
The first reason is that there may be cases where 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 "eyeballing" may be appropriate.
In such situations, having a flexible multi-point AF system becomes very useful.
The main goal of such systems, however, is not saving time. The purpose is rather to give the photographer the ability to capture moving subjects. This is especially important for wildlife and sports photographers, for whom the ability to use autofocus correctly is crucial, as it is for everyone who shoots dynamic subjects.
Let's say you want to take a photo of a child running. By the time you set the focus, the child will have long run away (forget about trying to change the composition after pre-focusing in this case).
Even with the very fast autofocus of modern systems, there is no way to take more than one frame at a time without changing the focusing paradigm. How can you use high shooting speed to then select one of the sequential frames?
Most DSLR cameras support, in addition to the aforementioned one-time autofocus feature, a very powerful feature - 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, automatic 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, 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 your chance of getting the best shot.
The advice that was most important to me when I was learning to shoot with autofocus. Since autofocus is done using sensors that detect it, it only works well when the focus point is with some kind of contrast!
For example, when I place the AF point towards the edge of the subject, the focus is instantaneous and very precise. 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 sharp it is seeing 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 decide whether your vision is perfect or not. This is only possible when you can see the edges of objects, and not when there is only a white wall around.
To reuse the previously selected focus, you can see what happened when I tried to focus on two various 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 will not allow you to take a photo until the sensors are confident that focus has been found.)
Most DSLR cameras have an AF illuminator, and some models can turn it on. This helps you focus in the dark. If everything is black, the camera faces the same problem as in tip #1, the sensor has no idea what is in focus and what is not. Remember, however, not to enable this mode in areas where flash photography is prohibited.
As it may seem, this is a solution to most problems; I gave money and got a simple way to improve autofocus. Fast - that is, having a maximum aperture (smaller aperture number, for example, f/1/.8), that is, the lens has a larger opening.
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 lens's maximum aperture potential, the easier the autofocusing process will be.
In fact, when using DSLRs low level with small apertures, such as f/5.6 lenses, usually kit lenses, autofocus will not work at any point except the center, even pro-class cameras can only cope with lenses with large maximum aperture potential.
In their early days, autofocus systems were truly hocus-pocus. Now we can’t imagine life without autofocus, but just recently everyone used it and didn’t even imagine that automation would be able to clearly capture the subject of shooting.
People first started talking about autofocus in the 70s of the last century. Then the German company distinguished itself Leica, which developed the first autofocus lens, and introduced in 1976 the first camera equipped with an autofocus system. She became Leica Correfot, shown as a prototype at the exhibition Photokina-1976.
But the German company was in no hurry to produce autofocus systems and sold the technology to the company Minolta, which, thanks to the effective implementation of autofocus in its DSLRs, by the mid-1980s. rapidly became a leader in photographic equipment sales. In parallel, other corporations were developing automatic focusing systems ( Canon, Seiko, Polaroid, Pentax etc.) and the technology reached the masses.
We won’t go into much technical detail about how automatic focusing systems work for now. But let’s try to tell you how they function.
Today there are two main types of autofocus: phase And contrasting, as well as their symbiosis, which is called hybrid.
Phase detection autofocus
This type of focusing is fully used in DSLRs. It is based on the principle of the phase difference of the light flux that enters the lens. The difference is determined by special sensors that are placed in close proximity to the camera matrix.
The principle of operation of the phase detection autofocus system is clearly demonstrated in the picture below. The light flux enters through the opposite edges of the lens to the main mirror, where it is divided into parts: part goes to the viewfinder, and another part goes directly to the additional mirror, which reflects the rays onto the focusing sensors. If the light rays, after passing through the mirror and focusing lens, are focused at one point, then the subject is in focus. If the lens is focused closer or further away from the subject, the distance between the rays will be smaller or larger accordingly. In this case, the processor comes into play, which calculates the direction and amount by which the focusing lens needs to be moved.
Even naked eye There is a direct dependence of autofocus performance on the lens aperture. Indeed, the more light that enters the front element of the lens, the more of it will be reflected and the better the autofocus sensors will work. In this case, it doesn’t matter how much you close the aperture - it will close to the set value only at the moment the shutter is released, and during focusing the aperture will be open to the maximum. Those. Having a lens with f/1.2-1.4 aperture in your arsenal, you can count on higher focusing speed and accuracy. On the other hand, this is offset by the fact that more fast lenses They have a more complex and massive lens system, which means that it is more difficult for the motor to move this entire mechanism. In addition, a large aperture implies a much shallower depth of field into which phase sensors need to penetrate. Bright to that example - one of the slowest (if not the slowest) lens from Canon - EF 85mm f/1.2L II USM.
The following illustration clearly shows the phenomena of back focus and front focus:
- focus closer – back focus;
- focus further – front focus.
The phase sensors themselves can be linear(horizontal And vertical) And crusades(incl. double crosses). We will look at them in more detail in upcoming materials.
Contrast autofocus
This focusing method is widely used in compacts and mirrorless cameras. They are not shy about installing contrast sensors in DSLRs - they provide focusing in LiveView mode when phase sensors cannot work.
The operation of the contrast autofocus system is based on the principle of comparing the contrast of the image that enters the camera matrix. The camera's processor analyzes the histogram and shifts the lens to see how much the contrast changes. If the contrast level goes down, the focus point will begin to shift reverse side. If the contrast increases, the focus point will continue to shift in this direction until it is possible to reach maximum value contrast. Those. the process continues until the focus point reaches maximum contrast and returns to the point after which its level began to decrease. In this case, the subject will be focused. The big advantage of contrast focusing over phase focusing is that with it there is no back and front focus.
To view, move the mouse cursor to the upper right corner and move the slider forward/backward (visualization - http://graphics.stanford.edu/courses/cs178/applets/autofocusCD.html)
Hybrid autofocus
Today, this type of automatic focusing system is becoming increasingly popular. And for good reason - it combines the advantages of both systems and eliminates their disadvantages.
It works approximately as follows: phase sensors, which are located directly on the camera matrix, provide primary focusing. Subsequently, contrast sensors are connected, which correct the difference in image contrast and finally focus the camera on the subject.
Perhaps one of the main advantages of hybrid autofocus systems is the absence of back and front focus. This is explained by the fact that focusing occurs directly on the camera matrix. Another important advantage is the compact size of the hybrid autofocus system and the absence of the need to adjust this mechanism. But there is also a fly in the ointment - in terms of speed in tracking mode, hybrid autofocus still does not reach phase autofocus.
If you want to learn more about the operation of automatic focusing systems (with formulas and calculations), write in the comments. If there are enough people interested, we will definitely write a separate material on this topic.
Article text updated: 12/13/2018
Many modern DSLR cameras have such advanced autofocus systems that it can often be difficult to understand how to use them. Whether we're shooting with an entry-level camera or a professional camera, to ensure sharp photos, we need to try to figure out how to use the different autofocus modes. Incorrect focusing or a blurry image can destroy the positive impression of the photo, and this defect can be corrected in the process of subsequent processing in graphic editor impossible. Some photographers convert their photos to black and white to hide focus issues. If we learn how to focus correctly, we won't need to resort to these kinds of tricks, we will get a much better result that our viewers will love. A clear image is what people want to see when they look at our photos today. Someone might argue that sometimes a blurry picture looks “creative,” but here we need to understand: it’s one thing when we blur a photo for a specific purpose, and another thing when we ruin a photo because we don’t understand the workings 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 obtain high-quality photograph, you need not only to choose the right shutter speed and autofocus mode, but also to be able to quickly rotate the zoom... Nikon D610 camera. Nikkor 70-300 telephoto lens. Settings: ISO 1000, FR-98mm, f/5.0, B=1/2500 second
In today's free photography tutorial, we'll cover the basics of autofocus modes on DSLR cameras. 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 look at a couple of examples for clarity. Since I myself now have a full-frame Nikon D610 camera, and previously had a cropped Nikon D5100 camera, more emphasis will be placed on the performance of DSLRs from this manufacturer. Well, I apologize to completely 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 differences between modern cameras and their film counterparts produced fifteen years ago is that now we don’t 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 the settings and retake the 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 can boast good autofocus capabilities. 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) systems: active and passive. Active AF works by sending an infrared beam to our subject and capturing its reflection (the “sounder” principle). The camera makes calculations and understands how far the object is from it, and sends a signal to the lens how much to adjust the focus. A nice benefit of the active focusing system is that it can work in very low light conditions where normal (passive) autofocus would fail. The disadvantage of “Active AF” is that this mode can only be used in stationary conditions, for shooting stationary subjects, and only works at short distances: up to 5-6 meters. If we take photographs using a Nikon or Canon flash that has an AF Assist function, it will work in active autofocus mode.
The “Passive AF” system is based on a completely different principle: it does not send an IR beam and does not pick up its reflection to understand the distance between the camera and the subject in focus. Instead, special sensors inside the camera are used to contrast definitions parts 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 “definition of contrast”? Without going into the jungle of terminology, this is a determination of sharpness in a certain area of the 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 begins to "hunt" over a uniform surface (for example, a white wall or some surfaces with a smooth transition of tones), this is because the camera needs objects with edges (contrast) separated from the background in order to understand how adjust focus.
By the way, if there is an AF-assist illuminator lamp on the front panel of our DSLR, this does not mean that the camera is operating in active focusing mode: all the lamp does is illuminate our subject, like a flashlight, i.e. The camera operates in “Passive A.F.”.
Many digital cameras, such as point-and-shoot cameras, camcorders and the like, most often use "contrast AF method" to achieve focus. At the same time, most modern DSLRs can be equipped with both systems for focusing correction: phase detection and contrast detection autofocus.
Since the “contrast method” requires light to hit the sensor, a DSLR camera must have its mirror in the raised position when determining focus, 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 focusing on stationary objects. Contrast-contrast autofocus often performs better than phase-detection AF, especially in low-light conditions. The advantage of contrast focusing is that to adjust sharpness it is enough to use any part of the image (including that which is at the very edge) on the matrix, while phase focusing requires the use of one or more focusing points of the DSLR. The disadvantage of the contrast method today is that it is relatively slow.
Many professionals are confident that camera manufacturers will be able to solve this problem in the foreseeable future, since autofocus speed when shooting video is becoming increasingly important for DSLRs and some mirrorless cameras (in particular, the Micro Four Thirds standard, 4/3) are already equipped with fast contrast AF. Modern mirrorless cameras of the highest price category have two autofocus systems: fast phase detection for working with good light and slow contrast for low light conditions. Some manufacturers, in general, managed to integrate phase sensor pixels 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 described 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. We just need to remember that focusing errors in a camera happen due to the lack of light passing through the lens and the type of focusing mode we have chosen (as explained below).
1.2 Focus points
Focus points are small empty rectangles or circles that we can find in the viewfinder of our camera. Manufacturers often differentiate between amateur and professional level cameras by integrating various systems automatic focusing. Entry-level DSLRs usually have minimal amount focus points, allowing you to achieve focus, and advanced SLR cameras are equipped with a comprehensive, highly configurable AF system with big amount focusing points. They are part of a "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 between different manufacturers, but also among different camera models. Here is an example of two different types autofocus with a different number of focus points and their location.
As you can see, the Nikon D5100 DSLR has 11 points, while the Nikon D810 has 51 points - a big difference in the number of sensors. Does the number of focus points matter? Absolutely - yes! And the point is not only that it is easier for us to compose a specific shot, focusing on a specific area of the image, but also because the AF system can more effectively track the subject in the frame (extremely convenient when shooting sports competitions and wild animals). Although, we must keep 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 AF system of DSLRs
let `s talk about various types auto focus points in DSLRs. As stated above, the number of points is not the only important parameter of an autofocus system. The point type also has critical value to achieve accuracy. There are three types of focus points: vertical, horizontal And crusades. 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 to work with. Therefore, the more cross sensors in our DSLR, the more accurately the AF system works.
That's why when a new model is announced SLR camera, in the review we can read something like: “The number of focusing points is X, of which Y is a cross type.” The manufacturer proudly emphasizes the number of dots, especially the presence of cross dots, if there are more of them in the new camera. 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 focusing points, including 15 cross ones, while the old lady has 39 points, 9 cross ones.
When we buy a new SLR camera that we plan to use for shooting sporting events or for photo hunting, we need to pay close attention for both of these parameters.
1.4 Other factors affecting the performance of a camera's autofocus system
As we can see, both the number of focus points and their type are important. Although, they are not the only ones that affect the operation of automatic focusing. 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 outside, but when we go into a dimly lit room, the lens begins to “hunt.” Why is this happening? Because, in low light conditions of the subject, it is much more difficult for the camera to measure the contrast differences in the scene. Remember that passive autofocus is entirely dependent on the light passing through the lens, and if the lighting quality is poor, then autofocus will not work satisfactorily.
Speaking about the quality of light, we must not forget about the features of the lens, and the fact that the maximum open aperture also has an impact on AF. If we shoot with old glass that has mold, dirt, too much dust, or has problems with front and back focus, then automatic focusing, of course, will not work very accurately.
This is why professional lenses at f/2.8 can focus much faster than amateur lenses at f/5.6. The f/2.8 aperture is the most suitable for high-speed focusing: the aperture is not too wide, not too narrow. By the way, lenses at aperture 1.4 usually focus more slowly than at f/2.8, since more rotations of the glass elements inside the structure are required to properly focus .
Focusing accuracy is important at such open apertures because the depth of field is very narrow. Ideally, the aperture should be between f/2.0 and f/2.8 for the autofocus system to function best.
Smaller apertures, such as f/5.6, will result in less light passing through the lens and making it harder for the autofocus system to work. For this reason, open apertures (with the exception of f/1.4) are preferable to closed ones.
It should also be added that all modern digital cameras focus with an open aperture, so no matter what aperture number we choose (for example, f/22), the aperture changes only at the moment of shooting .
Finally, the overall quality and durability of the autofocus system is of the utmost importance. For example, the top-end professional DSLR Canon 1D Mark III, designed for shooting sports competitions and photo hunting, after its release into 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 to get better system For automatic focusing in modern DSLR cameras, especially for shooting sports and wildlife, you should choose from Nikon or Canon (although other manufacturers are quickly catching up with the market leaders).
2. Auto focus modes of digital SLRs
These days, most DSLR cameras have the ability to shoot in a variety of focus-off modes depending on the specific situation.
It’s one thing when we photograph a portrait of a calmly sitting person, and another when we photograph a running athlete or a flying hawk. When we shoot a stationary subject, we focus once and take a photo. But if the subject is in continuous motion, we need the camera to automatically adjust the focus at the moment we take the picture. The good news is that our camera has a built-in function for efficient work in such situation. Let's look at each of the focusing modes in more detail.
2.1 Single-frame focus tracking mode
Single-frame tracking focusing in Nikon cameras is designated “AF-S”; in Canon cameras this type is called “One-shot AF”. And it provides a simple way to directly focus the lens. We select a focusing point, and the camera measures the contrast simply one point at a time.
If we press the shutter button or the assigned AF button (if such assignment is possible in our model) halfway, the camera is focused, but if the subject moves, the focus does not reset, even if we continue to press the shutter button halfway. That is, the focus remains “locked”.
Typically, in single-servo AF mode, in order for the shutter release to fire, the camera must first be in focus. Therefore, if it was not possible to focus, or the subject has moved, pressing the shutter will do nothing (due to a focus error). In some camera models it is possible to change the camera’s reaction to lack of focus (for example, on the Nikon D810 we can set the “AF-S Priority Selection” setting in the “Release” custom settings menu, which will allow us to take a photo even if the camera does not focus) .
There are some 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 setting the camera to AF-S mode for it to work. The same is true for the autofocus 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 DSLR cameras 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 absolutely necessary when photographing sports, wild animals and other non-stationary objects. The operating principle of this mode is based on analyzing the movements of objects and predicting where it will be in the next moment, and setting the focus to this point.
The advantage of this mode is that the focus automatically adjusts if the photographer or subject moves. All you need to do is continue to hold the shutter button (or the key assigned to AF, if there is an assignment option) half-pressed. The autofocus system will automatically track the subject. Compared to AF-S single-servo focus, AF-C continuous focus mode tends to have a lot of settings (especially on the most expensive DSLRs) and can handle complex tasks such as tracking subjects across one or more focus points.
2.3 Hybrid single-shot and focus-servo mode
Some cameras also have another mode called Auto Servo AF “AF-A” on Nikon cameras or “AI Focus AF” on Canon cameras. It is a kind of hybrid that automatically switches between single-frame and continuous focusing. If the camera detects that the subject is stationary, it switches to AF-S mode, and if the subject is moving, it switches to AF-C.
Cheap DSLRs have AF-A enabled by default and work fairly well in many situations. Many professional cameras do not have an Auto Tracking AF mode because it was designed for beginners.
2.4 Continuous focus tracking
The constant focus tracking mode, designated by Nikon as “AF-F”, was introduced by the company for the new Nikon D3100 and D7000 models. It is intended primarily for shooting in Live View format. In this mode, the camera tracks the subject and automatically adjusts the focus while shooting video. 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 perfect the “AF-F” mode. If you do not shoot video with a DSLR, then you should not enable this mode.
Many professional photographers in photography lessons for beginners note that most For some time, they have the AF-C continuous focus tracking mode enabled, and only when the camera cannot focus in poor lighting conditions do 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 different models it happens in different ways. 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 a Nikon D610 camera: press the AF mode button and simultaneously turn the control wheel.
The letter “C” appears on the auxiliary screen, which means the camera is operating in AF-C continuous focus tracking mode, switch to “S” - single-frame focus is activated. Pressed “M” - switched to manual control of camera focusing.
3. Auto Focus Area Modes
To confuse novice photographers even more, many DSLR cameras have menu items called something like “AF Area Mode”, which allow the amateur photographer to select several options for how focusing will work in AF-S, AF-C, AF- modes. A and AF-F.
For entry-level DSLRs, such as Nikon D3100 or Nikon D5200, settings can be changed through the menu, and 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 DSLR cameras Nikon D810 and Nikon D4S cannot reassign control of this parameter to other buttons). Let's see what choosing an auto focus area gives us.
3.1 Single point focus area
When we select “Single Point AF” mode in a Nikon camera or “Manual AF Point” in a Canon camera, we use only one focusing point through the viewfinder to achieve focus. That is, when we switch from one point to another with the joystick, the camera measures the contrast only in this particular area of the image, using vertical or cross sensors (depending on which one we chose). Many professional photographers recommend using single-point focus mode when shooting landscapes, architecture, and other stationary subjects.
3.2 Dynamic Focus Area Mode
In the “Dynamic AF” mode for Nikon or “AF Point Expansion” for Canon cameras, we select one focus point, and the camera first adjusts the focus according to it. Next, once the focus is set, if the subject moves, the camera uses surrounding dots to track it and keeps focus on the subject. We expect it to follow the subject's movement and keep it in focus while keeping the camera close to the initially selected focus point. If the camera selects surrounding/other points - this will not be visible in the viewfinder, but will be noticeable in the finished photo.
Dynamic AF mode works great when shooting fast-moving subjects like birds, as we have a hard time keeping the bird in focus while it's flying. Advanced DSLRs, for example, Nikon D7100, Nikon D7200 or Nikon D800, allow you to choose the number of points surrounding the main one: 9, 21 or 51 pieces.
Thus, when we want to monitor 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.
IN Lately 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 3D tracking mode is that the camera uses its built-in pattern recognition system to automatically read colors and follow the subject itself, and you simply compose the photo as the subject moves.
For example, we photograph a white heron walking among black birds. System 3 DTracking will automatically focus on the white bird and follow it even if the bird moves or the camera moves, allowing us to compose the shot .
If we compare the “Dynamic AF” and “3D Tracking” modes, then in the first case a certain number of points will be used, and in the second, all available ones will be used to track the subject. At the same time, “Dynamic AF” uses certain “zones”, activating only the surrounding focus points (as many as we selected in the settings). For example, we selected 9 points, tracking will work as long as the object is in the area of 9 focus points surrounding the main one. If the subject leaves this area, the camera will not be able to focus. But in 3D tracking mode, the camera will continue to monitor the object (the newly selected points will be displayed in the viewfinder), even if it moves significantly away from the initially selected point.
Professionals use the dynamic autofocus mode when photographing birds and wild animals, using a small number of points: 9 or 21 pieces. There are different opinions about 3D tracking, since it is not as fast as with, for example, 9 points of dynamic AF.
3.3 Automatic focus area selection mode
On Nikon cameras it is designated as “Automatic AF Point Selection”, on Canon it is “Automatic AF Point Selection” and is a “point and shoot” focusing method. The camera automatically chooses what to focus on. This is a complex system that can recognize the color of a person’s skin in a frame and automatically focus on it. If there are several people in the frame, the focus will be on the one closest to the camera. If there are no people in the frame, then, usually, the camera focuses on a near or distant object. If we have selected AF-S and Auto-area AF modes, the active focus point will be displayed in the viewfinder for a second, allowing us to confirm the area on which the camera has focused.
The same is possible with Canon cameras, but their mode is called “Automatic AF point selection in One-Shot AF mode”. It's hard to say why this mode is needed, since professionals like to control all the shooting parameters, rather than letting the camera do it for them.
3.4 Group focus mode
The latest models of Nikon SLR cameras, such as the Nikon D810 and Nikon D4S, have a new “Group AF” focus area selection mode. Unlike "Single-point AF", not one, but five focusing points are used to track subjects. This mode is better suited for setting the starting point for focusing and tracking subjects than Single-point AF or Dynamic AF, especially when we're talking about about photo hunting for small birds that constantly flutter from branch to branch and it can be difficult to catch them in focus and follow them. In such cases, “Group AF” can greatly help the photographer and produce better results than “Dynamic AF”, since it is more accurate and provides consistency from shot to shot.
How does group focus mode work? We see 4 focusing 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, which is more accurate). Once we've locked onto a subject, all five points are activated simultaneously to initially focus on the closest subject.
This is in contrast to “Dynamic AF” with 9 points, which has priority over the selected center point. If it was not possible to focus on the central one (low contrast), the camera will try the other 8 pieces. Initially, the camera always focuses on the central point, and only then moves to the other 8 pieces.
In turn, “Group AF” uses all 5 points simultaneously and tries to focus on the nearest subject, without giving any advantage to any of the 5 points.
Group AF mode is especially useful for shooting birds, wildlife and non-team sports. In the example above of the cyclists, if our goal is to focus on the athlete in front, Group AF would be a better option because this mode will allow the camera to follow the athlete closest to it.
Another good example: 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 catch focus. If we point 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, photographing small birds can be slightly difficult, especially in bushes, or if the branches they are sitting on are constantly swaying. Choosing the starting point of focus is very important, and the sooner we choose it, the higher the chances of catching the bird in focus and tracking it, especially if it suddenly decides to fly away. As stated above, in the “Group AF” mode, there are no advantages to any single focus point; all 5 are activated simultaneously. 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 mode will follow the subject, but again only if one of the 5 points is close to the subject. If the subject is moving quickly and we do not have time to turn the camera in the same direction, focus will be lost, just as would happen in the 9-point Dynamic AF mode.
Some photographers say that Group AF mode allows you to catch focus quite quickly, but no one has really measured whether it is faster than 9-point dynamic focusing. Perhaps the latter will be faster in some situations.
Another important fact to note is that when we enable Group AF mode while single focusing A.F.— 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 photograph someone standing between tree branches 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're photographing a group of fast-moving athletes and we need the camera to lock focus and follow the subjects' faces (rather than focusing on nearby objects), we're 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 autofocus modes for Nikon cameras.
When viewing images clockwise: Single-point AF mode, Automatic AF area selection (9, 21 and 51), 3D tracking and Group AF.
3.5 Other focus area selection modes
The latest DSLR models have new area selection modes, for example: “Face-priority AF”, “Wide-area AF”, “Normal-area AF” and “Subject-tracking AF”. These modes are used when shooting video with a DSLR 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 is slightly different in different cameras and may be changed in the future.
Canon also has its own autofocus area selection modes, for example, “Spot AF”, in which we can fine-tune the focus within the focus point. This mode is highly specialized; it can be found, for example, in Canon EOS 7D cameras.
3.6 In what cases to choose one or another type of automatic 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 a focus mode! To understand this better, let's make a table with examples (for Nikon DSLR cameras).
|
AF area selection mode |
Nikon Focus Modes |
||
Single-point AF |
The camera is focused only once and only at the selected focus point. |
The camera is focused on one selected point, and when the object moves, the focus is re-adjusted. |
The DSLR detects whether the subject is moving or stationary and automatically decides which mode to use: AF-S or AF-C. In any case, only one point applies. |
|
Dynamic AF |
Disabled, just works like single point autofocus. |
We select a starting focus point and, once the camera is aimed at the subject, surrounding dots are turned on to track its movement. In the camera menu you can select the number of auxiliary points. |
As in the previous case, but for a group of points. |
|
As in the previous case |
Instead of using a specific number of focus points, all possible ones are used and color recognition is used to track the subject. The photographer specifies a starting point, and the camera tracks the subject across the frame automatically, allowing him to recompose the shot without losing focus on the subject. |
Similar to the previous one |
|
|
The camera activates 5 focusing points and aims at the nearest object. If it determines that there is a person in the frame, it will focus on him. |
The camera automatically focuses on the nearest subject and follows him in the frame as long as he is close to 5 points. Face recognition doesn't work. |
Not available. |
|
|
Automatic AF area selection |
The camera itself selects a point depending on what is in the frame. |
The camera itself sets a point on a moving object and follows it. |
Similar to previous cases. |
Note to the table explaining the focus area selection modes above: in various models Some options may be missing.
3.7 Changing focus area selection modes
To understand how to change the focus area selection mode specifically for your camera, it is better to read the instructions. For entry-level DSLRs such as Nikon D3100 or Nikon D3300, you need to enter the “Shooting Mode Menu” section, and advanced cameras have a switch on the rear panel. Here, for example, is what the auxiliary display looks like on the Nikon D600 and D610 SLR cameras.
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've learned a lot of technical information about what each of the auto focus and AF-area modes are. Let's go through some more scenarios and examples to ensure we have a good understanding and grasp of the data presented earlier. The camera settings described below are taken for Nikon cameras.
4.1 Scenario No. 1 – Filming sports competitions on the street
Which autofocus mode and type of AF area metering will we choose when photographing, for example, football? Let's start with the choice correct mode focusing. Obviously, the AF-S single-servo focusing mode will not work, since we need the camera to focus constantly as long as the shutter button is half-pressed (or the button that we assigned to AF). Therefore we must use either AF-C or AF-A mode. Professionals want complete control of the shooting process, so they switch to AF-C continuous-servo autofocus mode in this situation.
What about AF area selection? Should we enable Single Point AF, Dynamic AF, Group AF or 3D Tracking? Professional photographers, when photographing sporting events such as football, basketball or outdoor hockey, will include 3D tracking, allowing the camera to follow the athletes while a person composes the shot. If it suddenly turns out that 3D tracking does not work correctly and makes mistakes often, then you can switch to “Dynamic AF” with a sufficiently large number of focus points, especially if we are standing close to the scene of action. The Group AF mode will only work well if we are standing very close to our subjects. Here is a set of focus mode settings for the described cases:
- Auto Focus Method:AF-C
- AF area metering mode: 3D Tracking, Dynamic or Group AF
- Custom Settings => Dynamic AF: 21 or 51 points
- Custom Settings => AF-C Priority Selection: Focus priority
4.2 Scenario No. 2 – Shooting people on the street
When we're photographing people posing outdoors on a sunny day, either focus mode should work well. If we chose AF-S, the camera will focus once as soon as we half-press the Shutter, so we just need to be sure that our subject doesn't move after focusing. By default, the camera will not allow you to take a photo in AF-S single-servo focusing mode if the focus is not achieved.
If we shoot in AF-C continuous focus tracking mode, we just have to make sure that the focus is set correctly before pressing the button. Also, AF-A is good for shooting portraits.
As for choosing the AF metering area, it is more convenient to shoot with “Single-point AF”, since the subject is motionless.
- Modeautofocus: AF-S, AF-C or AF-A
- AF metering area: single point
- Custom Settings => AF-S Priority Selection: Focus priority
- Custom Settings => AF-C Priority Selection: release priority
It probably goes without saying that we should always focus on the closest eye of our model, especially if she is close to us.
4.3 Scenario #3 – Taking portraits indoors
Shooting people inside a building in poor lighting can be a bit difficult. If the room is dark, we can switch to AF-S single-servo focus mode and let the assist illuminator assist us if needed. If we have an external flash, AF-S mode will allow us to turn on the red beam to adjust the focus.
You cannot use this function in AF-C mode. AF-A autofocus should also handle this situation, but professional photographers will prefer to turn on AF-S.
As for AF area metering, it is more convenient to use the central focus point for greater accuracy in low-light conditions.
- Autofocus mode: AF-S
- Metering: Single point AF
- Custom Settings => AF-S Priority Selection: Focus priority
4.4 Scenario No. 4 – photographing birds in flight
Bird photography is an extremely difficult genre of photography because it is difficult for us to predict their behavior and they often fly very quickly. As noted above, when photographing, it is better to select the “Continuous-servo AF” (AF-C) mode, and the focus area - either “Group AF” or “Dynamic AF” with 9 or 21 points (I would like to photograph with 21 points , but usually 9 pieces are faster). Professional photographers say they've tried using 51 focus points and 3D tracking, but these modes are slower and less accurate than using fewer points.
One of the photographers told me that 99% of the time he focuses on the birds on the central point, changing it only when the birds are sitting high on some branch. Again: center point focusing in most cases gives the best result. If we're shooting small birds and don't have time to set the starting focus point, we can try the Group AF mode (if available on your camera).
- Autofocus mode:AF-C
- AF area metering: Dynamic or Group AF
- Custom Settings => Dynamic AF: 9 or 21 points
- Custom Settings => AF-C Priority Selection: release priority
4.5 Scenario #5 – Shooting landscapes and architecture
All focusing modes are suitable for these types of shooting, but it is still more convenient to use AF-S, since we do not have objects to follow.
In low-light conditions, we won't be able to use the AF-assist illuminator function because the distances are very long. In this case, you can set the camera on a tripod and switch to Live View to focus on the bright object in our scene using the contrast method. If this does not help, there is only one thing left to do: turn off automatic focus and focus manually.
When photographing landscapes or architectural objects, we need to be more attentive to what our camera is focused on and remember that special meaning accepts the need for a clear understanding of depth of field (DOF) and hyperfocal distance.
Regarding metering the autofocus area, one thing can be said: we definitely need the “Single-point AF” mode to focus precisely on a specific point in our frame.
- Autofocus mode: AF-S
- Autofocus area selection method: Single point AF
- Custom Settings => AF-S Priority Selection: Focus priority
4.6 Scenario #6 – Photographing large animals
On safari, when photographing large animals, professionals prefer to use the AF-C continuous focus tracking mode and the Dynamic AF or 3D tracking AF area metering method, both of which work perfectly. Animals are usually not as nimble as birds (although sometimes they can move even faster), so if we are not shooting fast-paced events, it is better to use the Dynamic AF mode with more focus points or use 3D tracking.
- Auto Focus Mode:AF-C
- AF area selection: Dynamic Focus or 3D Tracking
- Custom Settings => Dynamic AF: maximum amount points or 3D
- Custom Settings => AF-C Priority Selection: release priority
Hopefully, the scenarios listed above will make it easier to understand when and how to choose a particular focus mode and focus area metering. Now it's time to go back to the table above and check if we understood everything well.
4.7 Scenario No. 7 – Photographing small groups
Beginners often ask what mode to focus in when we're shooting a group of several people. Before we talk about autofocus mode, there are some important things to discuss. If we use a lens with a standard focal length or a telephoto lens with an open aperture, we need to remember 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 will be in focus, and the rest will be blurred, unless they are standing in the same plane. There are two solutions here: either clamp 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. Let's imagine how people would need to stand if they pressed the back of their heads against a flat wall - this is how our models should be positioned.
As for the focusing modes, in the daytime they will all work well, but it is more convenient to use single-point focusing.
- Modesautofocus: AF-S, AF-C or AF-A
- Measuring method: Single point AF
- Custom Settings => AF-S Priority Selection: Focus priority
- 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 AF-S single-servo focusing mode and “focus priority,” we are telling the camera not to allow a photo to be taken if it cannot achieve focus. Professional photographers don't use AF-S very often, but when they do, they want their shots to be sharp.
For AF-C's continuous-servo autofocus mode, "release priority" works great in most situations: the camera fine-tunes focus but doesn't allow too long shutter lags, allowing the photographer to shoot when they want. For AF-C mode, there is no point in thinking about what priority to set: release or focus. In "release priority" the camera doesn't care whether the focus is good or bad (why do you need autofocus then?), but in "focus priority" it won't let you take a good photo until the focus is locked. If we need the focusing to be so precise, we switch to A.F.— SThen. We 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, cameras do an excellent job of autofocusing. But when photographers start shooting in low light, they face a lot of problems, especially if they shoot indoors. Here are some tips to make the autofocus system work better when there is not enough light:
1. Using the central focus point. It doesn’t matter whether our camera has 9 or 51 focusing points, we still focus on the central one, and not on the outer ones, if we shoot in poor light, because it works more accurately. There is usually a cross-type sensor in the center that works better than any other point on our camera.
But what then should we do with framing and composition if we have to focus on a central 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 DSLR cameras, 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 we recompose a shot, especially when photographing with a shallow depth of field and an open aperture. When we focus and then move the camera, the focus is likely to shift and we need to be careful to keep our subject sharp.
2. Turn on the AF-assist illuminator function on the camera or on 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 Servicing - AF-S.
3. Selecting contrasting objects and edges. Instead of trying to focus on a flat, monochromatic surface, look for “high contrast” objects that stand out from the background.
4. Add a little light or turn on lamps. Sounds simple, but if we have trouble focusing, what could be easier than adding a little more light or turning on more bulbs in the room? One professional photographer told how he had to photograph dancing 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 general lighting in the hall - all the problems resolved themselves, and he was able to take excellent photographs.
5. Watch your shutter speed. We may think that we have problems with focusing, but we must not forget that the shutter speed must be sufficient for handheld shooting. The rule for determining exposure time using the formula B=1/(2*FR) is described in detail in a separate photo tutorial on DSLR settings.
6. We use a tripod. By using a tripod, we can achieve more accurate focusing in low light without worrying about camera movement.
7. Let's use the contrast focusing feature in Live View mode. When we have installed the camera on a tripod, we can try focusing in Live View mode, in which, as we remember, we can use a more accurate method of focusing based on the contrast of objects in the frame. Many professional photographers note that whenever they have to photograph on a tripod, they try to use contrast focusing because it gives better 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– bright flashlight. If our camera model does not have a built-in autofocus illuminator, we use a bright flashlight and ask someone to shine it on our subject to try to focus. As soon as sharpness is captured, we switch to manual focus mode and turn off the flashlight, taking photographs “with the self-timer.” I've seen advice from professionals to use a laser pointer to focus when shooting night landscapes (don't forget that if you hit a person or animal in the eye, you can burn the retina).
9. Using manual focusing. This advice does not correspond to the title of the article, but we should be able to manually adjust the focus and not be afraid to do it. Sometimes manual focusing will be even faster than in automatic mode. Many landscapes, macro and architectural photographs are shot using manual focusing.
Photo 13. Another landscape shot with manual focusing. HDR of three frames. Nikon D610 camera. Lens - Samyang 14/2.8. Sirui T-2204X tripod.
P.S. Dear friends, colleagues and site guests! If you think that the article can be useful to other photographers, I would be grateful if you share a link to it on social networks, on specialized forums, or publish it on your blog. I just ask you to put an active link to the source! My wife spent the whole day drawing all these frames on the photographs... It’s impossible for her work to be in vain. Thank you! Good luck with sharp photos to you.
This article provides information about autofocus in SLR digital cameras, about what type it comes in, how to use it, and what to do about its problems (and how to identify them).
What is camera autofocus?
The autofocus of a camera is a device for automatically aiming the lens at the subject. To denote autofocus, the international abbreviation AF is used, which can be found in the names of autofocus lenses (more about them below) and in the camera settings menu.
How autofocus works
Everything is very simple: depending on the type of focusing, the camera reads in a certain way the data about what is visible through the lens. This data is then analyzed and, if necessary, the camera sends commands to the autofocus motor located in the lens. This motor moves the lens unit and produces focusing with the correction required by the camera. This process is repeated until the camera decides that focus has been achieved.
The same “screwdriver” on the bayonet mount of a Nikon camera
Note: Some Nikon cameras have a focusing motor that is located in the camera itself. These cameras are popularly called “carcasses with motors”, and the focusing mechanism itself is called a “screwdriver” due to their external similarity. The advantage of the “screwdriver” is that the camera’s autofocus will also work with old Soviet-era optics, despite the lack of a focusing motor in old lenses. However, keep in mind that old optics require modifications so that a Nikon camera can focus at infinity, which does not need to be done on Canon cameras (since the distance between the rear lens of the lens and the matrix in Canon is closer to given value on old SLR cameras).
Contrast autofocus
Contrast autofocus is the simplest type of autofocus in modern DSLR cameras.
This type of autofocus is quite reliable and is based on the simplest movement of the lens unit back and forth, and then determining the position when the image on the focus sensor was the most contrasting (that is, in most cases, sharp). An example of the algorithm for this aftofocus method is shown in the animation.
One of the disadvantages of this method is its extremely low speed. Also this method It only works if the image from the lens goes directly to the camera sensor, that is, the camera mirror is raised (usually this happens when the Live View preview screen is on).
Phase detection autofocus
Phase detection autofocus is a more complex mechanism that requires first understanding a little about the structure of a DSLR camera. Consider the camera operation diagram shown below.
Here the image hits the mirror, from where it is redirected upward and enters the viewfinder using re-reflection from a pentaprism (it is not in this diagram above). But the whole point is that the camera mirror is a little unusual, it is designed so that in a certain area in the center of the mirror, light penetrates through it, where this light is already waiting for another small mirror, which directs the central part of the image down, directly to the phase sensors autofocus If you switch the camera to Live View mode and raise the mirror in this way, you can see a recess under the place where the mirror was - this is where these sensors are located.
Phase detection autofocus sensors work as follows: light from different parts of the image hits the beam splitters (see diagram), from where a pair of beams reach the sensor through the lenses. The sensor is a pair of light-sensitive sensors. The point is that when the image is in focus (that is, on the separator the rays from the image converge to one point), on a pair of sensor sensors these rays fall exactly in the center. The advantage of this method is that you can see in advance in which direction the focusing needs to be adjusted so that the rays hit the center of the sensor, and moreover, how large the current error is.
From here advantage of phase detection autofocus: high speed.
However for precise work Such autofocus requires that the distance from the lens to the matrix be exactly the same as from the lens to the beam splitters. Therefore there is disadvantages: the mechanism requires fine tuning of the focus sensors and/or reflective mirror, the angle of inclination of which can greatly influence the operation of this mechanism. Incorrect adjustment may result in poor pictures due to persistently inaccurate focusing.
Hybrid autofocus
In modern advanced SLR cameras and mirrorless cameras, hybrid autofocus is found, which combines all the advantages of previous focusing methods. IN in this case focusing is carried out using a matrix, which itself already has phase detection autofocus sensors at the focusing points. Thereby achieves phase detection autofocus speed and contrast accuracy, which in this case slightly “brings” the focusing to the very exact value after the phase sensors have worked.
In this case, the camera can analyze the image from the matrix and focus in intelligent modes on the most significant parts of the frame for the plot (for example, on the faces of people in the frame). For the presence of such autofocus, see the description of the specific camera model that you want to purchase or already have in stock.
Autofocus problems
The process of correcting lens and/or camera problems when bad work autofocus is called alignment. Adjustment (from German justieren "to measure out") - the process of leveling structural elements along any axis; in a narrower sense, applicable to photography, this is fine-tuning the lens or camera mechanisms.
Lens adjustment
Quite often, the cause of inaccurate autofocus on a SLR camera is a problem with the lens. To make sure that the problem is in the lens, you should check the autofocus operation with another lens: if the camera focuses accurately with another lens, then the problem most likely really is in the lens and it needs to be taken to a service center for adjustment.
Adjusting the camera
Sometimes the source of the problem is the camera itself, or rather, the phase autofocus sensors. As mentioned earlier, this mechanism is prone to breakdowns at the slightest inaccuracy (the distance from the rear lens of the lens to the phase sensors must coincide as accurately as possible with the distance from the rear lens of the lens to the matrix).
To check the camera, you should again take another lens and check it for accuracy. If the camera’s autofocus is constantly “smeared” with another lens, then you can safely take the camera for adjustment. Or both lenses, hehe. No, well, if the second lens that you borrowed, for example, from friends, works fine on their camera, then the problem is in your camera.
You should know that the service center can adjust your camera and lenses to each other, so you can bring the camera with all your optics. Usually, a good service center keeps a perfectly adjusted reference camera and the same lens; the lenses themselves are adjusted on such a camera, and the cameras are adjusted on such a reference lens. Or they can adjust your camera to match your lens, but this is not very reliable if you are considering expanding your lens fleet.
You should also remember that advanced SLR cameras have the option of setting phase detection autofocus for each autofocus lens. That is, you programmatically give the camera a command that, say, “with this lens, make an autofocus correction closer, and with this lens, make it further away.” How to determine the correctness of the correction you specified is below.
Determining the nature of autofocus problems: front focus and back focus
To determine the correction in the camera options (and simply to diagnose autofocus problems), you should know that incorrect operation autofocus is divided into two types: “undershoot” and “overshoot” focus (front focus and back focus, respectively). To determine this defect, you can use special autofocus adjustment targets, of which there are plenty on the Internet. They should be printed and focused at the center of such a target. Before doing this, do not forget to completely defocus the camera somewhere far or near, so that it does not have any “indulgence” when trying to focus on the target.
Personally, from my experience, I will say that the autofocus of my camera almost equally missed the focusing target on both lenses, which clearly indicated a problem with front focus with phase detection autofocus sensors. I had to take it for adjustment.
Be aware of the focus point you use. Usually this is the central point, however, in the settings it can be changed to any other point/group of points, and then the camera may, for example, try to focus on the left side of the frame, while you have positioned the main subject in the center or on the right.
Look for contrasting objects in the focus area. The fact is that any autofocus will not understand what you want from it if you focus on a perfectly (white/black/any other color) object without any texture or detail.
If there are no suitable contrasting objects, aim at an equidistant contrasting object, and then frame the frame (move the camera’s gaze to where you originally wanted). This method is very helpful in difficult situations, for example, sometimes it is easier to focus not on the perfectly blue sky in the center of the frame, but on the edge of the cloud on the left, and then re-transfer the ideal blue background to the center of the frame. At close distances, use this method carefully, since, for example, the distance from the camera to the face of a person standing close is very different from the distance from the camera to his feet.
For very dynamic scenes, use autofocus tracking mode(Canon calls it servo focus). In this mode, the camera will periodically send signals to the camera to focus, thus increasing your chances of getting a focused photo on your subject. For example, I actively used this option when taking macro photography of working bumblebees, which do not stop in one place for more than one second. Although any autofocus is bad for macro photography (more on this below), and I got very few frames that were not rejected, but for shooting, say, a cyclist who is riding towards you - this is just the thing!
Intelligent Autofocus Mode It will choose the focus points for you. According to my observations, my camera in this mode selects the closest brightest object and activates the focus points that it covers. This mode designed for those who really don’t want to worry about autofocus =).
For macro photography at high magnification, autofocus is contraindicated, since the depth of field is usually so shallow that the camera cannot “catch” it. Thus, the lens begins to move back and forth in search of focus. You yourself will understand that shooting macro with your hands is more convenient, although not easy. Moreover, for a large macro shot it is easier to focus not by focusing, but by simply moving the camera closer or further from the subject.
With THIS magnification, you can forget about autofocus. About handheld shooting without flash, by the way. Expanding the autofocus capabilities of Canon cameras
In order to expand the capabilities of autofocus (and not only) I advise you to install the Magic Lantern firmware. During installation, you may need to update the firmware of your camera model to latest version by downloading it from the official Canon website. Then follow the instructions to install Magic Lantern.
I’ll say right away that there are similar firmwares for owners of Nikon or other brands of cameras; you can find a list of them.
Magic Lantern offers software scenarios for using autofocus, such as:
- autofocus trap (focus trap): the camera automatically takes a photo when any moving object, such as a bird, enters the field of focus;
- focus point patterns: now you can select not only single AF points or all at once, but also separate groups (all top, bottom, right, left, etc.);
- follow focus: manual control of auto focus with constant speed, can be useful when the video depends on the subject moving towards/away from you;
- moving focus (rack focus): the same thing, but a completely automated process, select the initial focusing distance, the final one - and go!
- focus stacking: an extremely useful option for macro photography, it allows you to take several photos with a shift in the focusing distance, and later you can combine these photos in any popular photo editor into one photo with a huge depth of field and detail for macro photography.
Conclusion
Camera autofocus is a difficult topic that you won’t be able to understand well “with one kick,” especially if you have any problems. If you get blurry photos on your DSLR, I advise you to do this before taking the camera to the service center. If the tips given in it helped you achieve high-definition images when manually focusing or focusing on the screen (contrast), but automatic focusing through the viewfinder (phase) continues to miss, feel free to take the camera to a service center!
Let's start with what autofocus is. This is a system that ensures automatic focusing of the camera lens or video camera on the object (or several objects) being photographed. Autofocus is most often referred to as AF.
There are two autofocus operating modes: passive And active. The point is that the system needs to determine the distance from the focal plane to the subject, and active autofocus achieves this through elements that interact with the subject (ultrasonic or infrared locators), while passive autofocus does not interact with the object itself and does not emit anything - it only analyzes light beams entering the camera.
Autofocus performs all its work in a matter of moments and practically without the direct participation of the photographer himself. This device is provided in all modern cameras and differs in type. As a rule, the following types are distinguished:
- Phase detection autofocus
- Contrast autofocus
- Hybrid autofocus
Let's take a closer look at each of them. Job phase detection autofocus is based on the use of special sensors that collect rays of light from scattered fragments that arrive at them from different points in the frame thanks to systems of mirrors (in some devices they are replaced by lenses). After this, all the light is divided into two streams and sent to the photosensitive sensor. The final alignment occurs at a certain moment when the separated beams are at the distance specified by the sensor device. Having calculated the required distance, the device itself determines how to change the position of the lenses in order to obtain an image of better quality. To the irrefutable advantages of autofocus phase type You can safely attribute the accuracy and speed of focusing, this is especially important if you are shooting a moving scene. A large number of sensors literally monitors the image, achieving maximum quality. Phase AF is used in mirror systems.
The next type of focusing is contrast autofocus. Its work is based on special light-sensitive elements that conduct research into the contrast of the scene being filmed. Accurate focusing occurs at the moment when the image acquires the sharpest contrast and sharpness that differs from the background. To achieve best result the microprocessor of such devices can shift the lenses from their original position. The advantages of this type of autofocus include simplicity, fairly small size and the absence of the need for any additional sensors. Due to the features of this system, it is used in point-and-shoot cameras, cameras of modern smartphones, etc.
Another species that deserves the photographer’s attention is hybrid autofocus. The original idea was to combine passive and active AF. Modern developments of hybrid autofocus are based on a combination of phase and contrast technologies. This type of autofocus is now being implemented in mirrorless systems, where this type of AF shows more convincing results than the contrast AF that was used before.
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