Complete Guide to Autofocus and AF Modes Part 2

In our Complete Guide to Autofocus Part 1 you learned how autofocus points work and found out about the autofocus system types—active as well as phase detection and contrast detection passive AF systems—and which ones of them are used nowadays.

Since the topic of autofocus is so wide and tends to be a bit complicated for most of photographers, we decided to divide our story into a couple of parts. Today we will talk about the focus modes available in modern DSLR cameras and explain you how they are different and which one you should use in certain situations.

There are two common situations in photography that have to do with focusing. It’s whether you are making a photograph of a still subject—landscapes, cityscapes, architecture, models, and so on—or a subject in motion, which can be cars, people, animals, etc.

Back in the old times SLRs either didn’t have any AF features or only had a simple single point AF system, but modern DSLRs let you enjoy advanced AF technologies that track moving subjects or even automatically change the AF mode depending on whether the subject is still or moving. Let us tell you a bit more about every of these modes.

AF-S/One Shot AF

The first focus mode is something that is called AF/S or Single Area AF in Nikon cameras and One Shot AF in Canon cameras. Hence its name, it works really simply and straightforwardly. When you half-press the shutter release button, the focus will be locked in one focus point. Even if the subject moves, the camera will not refocus automatically.

Another interesting thing about this mode is that often the camera won’t take the picture—even if you press the shutter button—unless the focus is set and locked in that focus point. This is especially helpful when there’s almost no light and your camera cannot focus in any other focus mode.

In this mode your camera will use AF assist beam in order to focus correctly, illuminating the area in front of the camera. The same way, your flashes with AF assist beam will work only in AF-S/One Shot AF mode.

Continuous AF-C/AI Servo

The focus mode which is called Continuous or AF-C in Nikons and AI Servo in Canons is great if you tend to make photographs of sportsmen, animals, children, and any other moving subjects.

Simply keep the shutter release button half pressed after focusing on a certain area and your camera will analyze the subject and will track their movement, automatically refocusing on the same area.

AF-A/AI Focus AF

Although not available on some entry-level cameras, AF-A in Nikons and AI Focus AF in Canons are an interesting mixture between the single area and continuous focus modes. When this mode is on, your DSLR will learn whether the subject is static or moving and will automatically choose between the best focus mode for this situation.

AF-F

AF-F, or Full-time Servo AF, is a brand-new focus mode for videos available only for Nikon users. In this mode your DSLR will predict and track the subject, focusing correctly, depending on their movements when you are shooting a video in Live View mode.

This is an excellent concept, but sometimes AF-F still functions pretty strange, especially on older firmware versions. Keep it mind when shooting videos on Nikons and choose other focus modes if you are having problems with AF.

Conclusion

AF-A/AI Focus AF hybrid mode works really well and may be the best choice for beginner and enthusiast photographers, whilst professionals may consider using AF-C/AI Servo modes and switch to AF-S/One Shot AF when there’s not enough light.

Program the AF mode button on your camera body in a way which is comfortable to you and change between the focus modes when necessary.

Our next article about autofocus will feature everything about the AF area modes and their correct usage according to different situations in photography. Stay tuned!

We hope that this article was of help to you and we’ll be glad to answer your questions in comments. Feel free to shoot us a message!

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