I am still finding photographers who don’t make the best use of their mirrorless cameras by sticking with old-style thinking about which AF operation mode to use, servo or one-shot.

Perhaps the biggest change for me and many photographers who shoot with mirrorless is the change to servo AF for most photos.

I was pleased to see the end of AI focus on the earlier mirrorless models, but scarily it’s returned on the latest EOS R6 Mark II and EOS R8. Here’s an explanation of which to use and why.

Servo AF

In the DSLRs this used to be called AI servo, but now the AI has been dropped from the name. Servo AF focuses on the subject and tracks it right up until the exposure is made, there is no lock of the focus. Without a focus lock and clever subject detection it means that I get more in focus shots for portraits, sports, street, wildlife and any genre where the subject moves, even slightly.

Uniquely with mirrorless and subject detection, the camera identifies the subject and then you can recompose the frame while keeping your finger on the shutter or AF-ON button. Your camera will automatically move the AF point to keep on the subject.  Quite possibly the biggest and most important change over DSLR.

One-shot AF

One-shot AF focuses on the subject, and when the subject is in focus the focus locks and stops driving the lens. Once the lock happens you can recompose the frame. Commonly this is the focus – lock – recompose technique referred to in many books and online content. Though now it’s largely not needed.

If you photograph purely static subjects, buildings, landscapes then you may want to use one-shot AF. Personally I only ever set my camera to one-shot AF on workshops to explain why I can always use servo AF.

Manual focus

This is my second most used focus method. For product shots, macro of static things I switch to manual and use the focus peaking and focus guide tools to ensure I get sharp focus.

AI Focus

I really hoped this was gone for good… but it’s back as a mode you can choose for the EOS R8 and EOS R6 Mark II. It’s also the only mode when your camera is set to green square full automatic mode. The problem is that you still have no control over when the camera switches between one-shot and servo, and with mirrorless it’s worse than DSLR. The camera AF points change colour for the different modes, but also in servo AF the AF points will move place to track a subject, but not in one-shot.

Imagine this, you aim the camera and focus, then recompose as the focus has locked. You then recompose the frame, causing the camera to switch to servo AF and track the initial subject changing the focus as needed as whole area AF tracking also becomes active as you are using servo AF. You don’t get focus lock that you expected. Perhaps the only good thing is that the AF points change from green to blue when the switch happens.

Continuous AF and Preview AF

Continuous AF and Preview AF are the same thing, you’ll see Continuous AF used on EOS R / RP / R5 / R6 and then it is renamed Preview AF. When enabled this is the setting that eats camera batteries. While the camera is switched on the lens is constantly driven to focus on a subject, but preview AF is not doing the focus when you press the shutter. The thinking is that if the lens is close to in-focus before the shutter is pressed then it is easier for the camera to acquire the subject using one-shot or servo AF. I turn it off on all my cameras for about 50% longer battery life and use the pre-focus tip I mentioned before.


Advent Calendar of Tips

This year I’m writing a quick tip each day up until the 25th of December, here’s some of the others I have already posted.


About the author

Full-time photo tutor and photographer. I love to share my knowledge and skills to make photos, videos and teach others. I write books and articles for photo magazines and I always have at least one Speedlite flash in my camera bag