WHAT is a back button AF and when do you use it? I’m not sure if all camera models have the option to transfer the autofocusing button at the back instead of the one in the shutter button. But I’m quite sure mid level to pro cameras have it.
Generally, the default button of AF in the shutter is the best position for majority of shooting scenes. It’s like cocking the gun and shooting it in one motion. When you’re shooting sports, events, photojourn and other genres that require quick action, it really is advantageous to keep the AF button in the shutter.
In cases when you do a planned shot, may it be product, food, landscape and the rest, back focusing becomes a solution. It allows you to take the shot without refocusing since the AF is disabled in the shutter button. This enables you to focus your attention to lighting and composition. However, when you’re mounted on a tripod, you lose the agility to focus and reframe.
Let’s say you are shooting a landscape scene and your camera is mounted on a tripod. You try to find an object to focus that is positioned about a third of a distance of the entire depth that you are planning to capture. The object happens to be positioned outside of your focusing points.
What you do is focus the object by pointing your camera, not minding the composition at first. Once done, reframe and take the shot. If you intend to take more shots with varying exposures, no need to focus again, just take the shot. This only applies if both the camera and focused objects stay in the same distance.
Given the same situation, if the autofocus is enabled in the shutter button, you have to release all the lock knobs in your tripod and refocus on the object again, then reframe the shot right after you locked all the tripod knobs.
All these steps are just to test a different exposure. However, you can always turn the autofocus switch in your lens to manual to prevent refocusing. Unfortunately, that switch in your lens is not designed to take high frequency of use.
When I’m shooting food and products, back button focusing is very much useful to me since most of the problem after focusing involves lighting. I also use it when shooting in studio so I don’t have to keep on nodding to refocus every time I take a shot.
Learn more about back button focusing at grp.ph/forum. Keep on shooting, everyone!