Focusing Techniques

 

Focus & Recompose 

Use when chosen focusing point does not coincide with object (=location on the subject) where the focus needs to lock - for desired composition.

Place focusing point on object of interest, focus, shift camera slightly laterally  to get desirable composition and shoot. 

Back Button Focus 

Standard focusing

When using Focus & Recompose with traditional shutter half-press focus, one has to focus, recompose, shoot, but once shutter has been pressed to take the shot, focus is lost, so will need to move camera again to lock focus & recompose again.

When using focus & recompose (using standard focus in single shot mode) on a subject that may move, any sudden movement before taking the shot may upset focus, requiring focus to be re-acquired. 

When using focus & recompose with continuous focus for a subject that may move, this technique will not work with traditional shutter half-press focusing, since as soon as the camera is moved slightly to recompose after acquiring focus, the focus will keep adjusting continuously.

Back button focusing

With back button focus, once focus has been acquired, one is free to recompose and shoot, as many times as needed without losing focus, as long as there is no change in the relative distance to the subject.

Using back button focusing on subjects that may move suddenly, allows combining advantages of both single shot & continuous focusing modes with the focus and recompose technique. Once focus has been set, as long as there is no motion in the subject, one may recompose and shoot as many times as needed similar to shooting in single shot focus. If the subject moves, one can easily press the back button and re-engage focus. Keeping the back button pressed allows seamless switch to continuous focusing mode.

With inputs from:

https://fstoppers.com/originals/back-button-focus-what-it-and-why-you-should-be-using-it-203806