Obviously, probably the most important aspect of any good photograph is whether or not a subject is in focus. Without that, the image is no good. Beyond general focusing, there’s targeted focusing, which is important, but not as important as the photo being sharp all over. Targeted focusing is more of a stylistic consideration.
Back in the day, we all were forced to manually focus our cameras, but today, we can sit back and take advantage of the very accurate and handy auto focusing technology that the camera gods have come up with. Basically, the camera does most of the work and it does a very good job of it at that. The most helpful times a photographer can use auto focus is when subjects in a scene are moving. With the continuous auto focus feature that most camera manufacturers offer these days, cameras can track a moving object and keep that object in focus. I’m sure you can see the benefit of that.
Personally, I use my Canon Rebel T7i’s auto focus for about 95% of my shots. I do a lot of landscape, still life and food photography and I like to establish the focusing distance right off the bat. I use back-button focusing, which helps tremendously in the situations I find myself in. So whether it be using a continuous auto focus feature or the one shot auto focus feature, my Canon DSLR camera has me covered.
To allow continuous auto focus to be used on your camera, if you’ve got a higher level Canon, you’ll need to enter the menu setup area and set Continuous Autofocus to Enable. My T7i doesn’t seem to offer this option, so I’m assuming that’s because I’ve got the no-frills version of Canon camera.
On my T7i, to set which version of auto focus I’d like to use, I’ll press the right arrow button on the back of the camera. This is the one that has the AF written on it. When I do that, the AF Operation screen will appear with three offerings. From left to right, they are One Shot, AI Focus and AI Servo. To read up on what each of these means, please take a look at this post. For now, I’ll simply tell you that if you’ve got a moving subject and you’d like to track that subject to keep it in focus, you’ll need to choose the AI Servo option. Then, when tracking the subject, you’ll need to keep the shutter button pressed half way down. That will put the camera in “eternal focusing” mode, which will keep it focusing on whatever object it’s currently being pointed at. If you’re using the back-button focus configuration like I am, I believe you should just keep that back button pressed all the way as you’re tracking your subject. Back-button auto focus isn’t optimal for sports and action photography, in my opinion.
For non-moving subjects, it’s much more appropriate to use the One Shot auto focus option. When using this setting, you can easily frame your scene, press the button to focus on your subject and then take your shot. If you’d like to focus in on your subject and then reframe the scene, that’s just as easy to do. Just be sure to only move from side to side when reframing, as any forward or backward movement will knock the subject out of your intended focus.
The reason you wouldn’t want to use continuous autofocus when capturing still life photos is because the camera may want to continuously focus on the non-moving subject. That’s not ideal because what the camera decides to ultimately focus on may not be predictable. It’s much better to choose the correct autofocus mode when it comes to still life photography. It’s the best setting to take advantage of when focusing on a still subject and then recomposing for a more styled photograph.