Rear-button focus moves the auto-focus from the shutter button to a button on the back of the camera. It's useful for a lot of use cases, but is especially helpful with older DSLRs that have trouble focusing in low light, and subjects that are in (or moving around within) a crowded scene.
You set the focus with the back button, then snap away without waiting for your camera to refocus every time you depress the shutter.
For fireworks, I'll focus near where I expect them, then adjust manually with the first few displays.
Aircraft that are moving slowly or horizontally across your field of view, especially if there are a lot of background objects, can be easier to handle with manual focus (or at least back button focus).
Fireworks, aircraft.
NOTE: rear-button focus is very helpful!
Rear-button focus moves the auto-focus from the shutter button to a button on the back of the camera. It's useful for a lot of use cases, but is especially helpful with older DSLRs that have trouble focusing in low light, and subjects that are in (or moving around within) a crowded scene.
You set the focus with the back button, then snap away without waiting for your camera to refocus every time you depress the shutter.
For fireworks, I'll focus near where I expect them, then adjust manually with the first few displays.
Aircraft that are moving slowly or horizontally across your field of view, especially if there are a lot of background objects, can be easier to handle with manual focus (or at least back button focus).