Aperture question

Originally Posted by hark

I've never used a D3500 or D5100, but back button focus is designed to be used in AF-C. What that means is the camera will continually focus on a moving subject as long as the back button is held down. If a subject is stationary, then it's suggested to focus with the back button, remove the thumb, recompose, and fire the shutter. So when used this way, it simulates AF-S (which is for stationary subjects), and the focus point doesn't change.

But if you are shooting in AF-C with back button according to this video for the D5100, there isn't any way to focus and recompose without the focus point changing (because it's set for AF-C which is continuous AF). It might be one of the downsides to the D3x00 and D5x00 bodies though.

The d5100 does have a menu A1 where af-c mode can be set to release priority. The default is focus priority. So the d5100 should be able to use the bbf technique as intended (as Cindy described). I don't have a d5100 though so I can't confirm it works but going by the manual, it should work.