We achieve perfect focusing accuracy. Autofocus accuracy check and fine-tuning

What if you systematically get fuzzy frames? Is the technique to blame or the reason for your actions? This article will help you figure it out. In it you will learn how to check the accuracy of the focusing system of the device and configure it to get sharp shots.

Nikon D810 / Nikon 85mm f / 1.4D AF Nikkor

I would like to say right away that in most cases it is not the camera that is mistaken, but the person working with it. So, for starters, it’s worth looking for the cause of errors with focusing in your own actions with the device. In recent lessons, we talked about how to work with different autofocus modes and with focus points . This knowledge will help you in practice. It will also be useful to read an article on how a novice photographer to evaluate and improve the quality of their own work. Autofocus can be wrong when working with insufficient lighting, and when shooting complex, diverse frames (the camera will not know what it should focus on). Such focusing flaws can be avoided simply by adjusting the apparatus according to the shooting conditions. For example, the choice of the AF-C continuous focus mode and 3D tracking of an object when shooting sports will allow you to get much more sharp frames than working with single-frame focus. But there are focusing errors that occur systematically, regardless of the shooting conditions.

Back and front focus

In SLR cameras, the phase type of autofocus is basic. It is with him that you deal, working through the viewfinder of the camera. Phase focusing occurs using a separate sensor installed in the camera. As you can see, this is a complex system, and sometimes it can work inconsistently.

The consequence of this will be systematic autofocus errors called back and front focus. In the case of back focus, the camera constantly focuses not on the subject being shot, but behind it. In the case of front focus, on the contrary, the camera constantly focuses in front of the subject. Please note that the presence of back and front focus can be said only when the camera makes a mistake with focusing each time in the same direction. If one frame is sharp and the other is not, then the problem should be looked for elsewhere.

Back focus: the focus was on the girl’s face, and the sharpness ended up behind her on the fence.

Particularly terrible is the problem of back and front focus when working with aperture portrait optics. There, the depth of field will be very small, therefore, any, even minor focusing errors will be very noticeable in the photo. For example, the sharpness in the frame is not on the eyes of the model, but on the ears. On the other hand, if you are a happy owner of a whale lens or universal zooms that do not shine with high aperture, you can sleep peacefully. Indeed, even if your camera has back- or front-focus, you most likely will not notice this, because focusing errors will be compensated by a large depth of field.

Contrast auto focus

In the SLR camera, in addition to phase focusing, there is another type of autofocus - contrast. You activate it, including the Live View mode and vising the picture through the screen of the device. With contrast autofocus, there can be no back and front focus, since it does not require separate sensors to work, focusing goes directly along the matrix. Thus, if the phase focusing regularly “smears”, try switching to Live View and working with contrast autofocus. It works a little slower, but gives more accurate results.

Checking Focus Accuracy

How to check the camera for back and front focus? An exact conclusion about the presence or absence of these shortcomings can be given only by an authorized service center of a manufacturer of photographic equipment. However, the photographer can make a preliminary assessment of the accuracy of the focus. We offer a simple algorithm for such verification.

First, prepare the camera.

1. Insert the battery and memory card into the camera. Turn on the camera. 2. Check if autofocus is on.

On entry-level models (such as the Nikon D3300 and Nikon D5500), autofocus is activated by a switch on the lens. It should be in position A.

On advanced-level cameras, there is a switch on both the lens and the camera. The letter M stands for Manual focus. Abbreviations A (Auto) or AF (Auto Focus) indicate auto focus. To enable auto focus, both switches must be in the appropriate position.

3. Press the Menu button, under “Image Quality” select “High Quality JPEG”. If you know how to work with RAW, you can use this format.

4. Turn on Mode A (Aperture Priority). If you know how to work with manual mode M, you can use it. Open the aperture of the camera to the maximum value. Everything is simple here: the smaller the number representing the diaphragm, the more open it is. In the case of the whale lens, you will most likely have to deal with an aperture value near F5.6. 5. Set the minimum sensitivity value. Usually it is ISO 100 or 200. So test shots will be clean, without digital noise. 6. Now - the most important thing! Choose a single-point focus mode. In the camera menu, it may be called “Single-Point AF”.

On entry-level cameras (Nikon D3300, Nikon D5500), the selection of the autofocus zone modes is carried out through the menu called up by the i button. In the appropriate paragraph, you just need to choose the best option.

On advanced Nikon cameras (starting with the Nikon D7200), the autofocus zone modes are selected as follows: hold down the button combined with the AF / M switch and rotate the front control wheel. In this case, on the information display you will see how the focus area modes change.

7. The point is small - download and print on any printer a special target for checking the accuracy of focusing.

Targets are of different types, but the proposed option is perhaps the most popular. In principle, you can check the focus, say, by the usual ruler (how - it will become clear later), but on the target it is much more convenient.

Checking autofocus

So, the camera is configured, the test target is printed. It's time to act!

It is best to mount the camera on a tripod . Without a tripod, such a check would be extremely inaccurate and non-indicative.
Provide adequate lighting for shooting. It’s best to shoot by the window during the day. You can use the flash (both built-in and external).
Put the target on a flat surface, and place the camera at an angle of 45 degrees to it at such a distance that the target occupies a significant area of ??the frame.
Choose the center AF point. Focus exactly on the target - on the inscription Focus Here (Focus here). A thick black line with this inscription should be located in your frame strictly perpendicular to the optical axis of the lens.

Take a few frames. Do not use continuous shooting, focus again after each shot. Remember that after focusing, in no case can you move the camera, change the shooting distance. If you are dealing with a zoom lens, test it at different focal lengths. I note that it is most convenient to conduct testing from a focal length in the region of 50 mm, and you can start with it.
View received frames. To better consider them, do this not on the screen of the camera, but on the computer monitor. If on all frames you see the same systematic focusing error, then most likely you have found back- or front-focus. To worry about this is not worth it. This is easily fixed at the service center. And owners of advanced cameras (starting with the Nikon D7200) can adjust the focus directly in the camera menu

Exact autofocus operation. Back and front focus are missing.

Back focus: sharpening is farther than necessary.

Front Focus: The sharpness is closer than needed.

Fine tune autofocus

Advanced cameras (starting with the Nikon D7200) have a function for fine-tuning autofocus, which will help you get rid of problems with back and front focus, fine-tune the focus system. The convenience of the function also lies in the fact that the device remembers the settings separately for each specific lens. Say an error occurs with one of your lenses. You will be able to make adjustments just for him, and they will not affect the work with other lenses. When the lens is mounted on the camera, it will automatically apply corrections corresponding to it. Please note that fine-tuning the autofocus will work only when focusing through the viewfinder of the device (during phase focusing). When working through the Live View screen, it is not involved, and there will be no need for it, because in this case a contrast type of autofocus is used, Let's see how the autofocus fine-tuning function works. Find the item “Fine tune AF” in the camera’s menu.

Fine-Tuning Autofocus Menu on the Nikon D810

The first item of this menu, as the name implies, allows you to enable or disable this function. The default menu item allows you to enter the AF fine-tuning value, which will be applied when a separate setting has not been created for the lens mounted on the camera. It makes sense to make such a setting if the device is systematically mistaken with focusing with all lenses.

The last item - “Display saved values” - allows you to see all the corrections stored on the camera for various lenses. You can make an autofocus setting for each lens you have, and it will be saved on the camera. Through this menu you can see all the corrections you have made. In the same paragraph, you can delete unnecessary settings. It is possible to enter your identifier (from 00 to 99) for each lens. This is useful if, for example, you use two identical lenses and make autofocus settings for each of them. Such an identifier will help distinguish you from each other in this menu. The most important menu item is “Saved Value” . It shows what fine-tuning value is currently applied, and makes it possible to change it. Once in this menu item, you can fine-tune the AF operation with a specific lens (currently installed on the device).

Fine tune autofocus

To make the necessary settings, first you need to make and study test shots (as described above). If the focus is on the test frames behind the object, you need to make a negative correction, and if in front of the object - positive. The difficulty lies in determining the desired amount of adjustment. You can find the optimal value using test frames. After making the approximate settings, just take a series of test shots and check whether the lens is now in sharpness. If not, make the appropriate corrections.