Rear button focus was never an issue before auto focus digital cameras came along. If we wanted to focus a lens it was done by rotating the focusing ring on the lens. Once the lens was focused it would never change focus until the photographer re-focused the lens on a different area. Pretty simple.
With the advent of the digital age things became a little more complicated. Modern digital camera adjust focus by holding the shutter release half way down. Each time you press the shutter release the lens is refocused. This is no longer the best way to do this. The lens in continually refocusing depending on where the focus spot is aimed. In order maintain sharp focus, the shutter release has to be held halfway down as the subject moves in the viewfinder. There is a better way.
Modern digital cameras have the built in ability to use another button to exact focus. On the Nikon brand, this button is called AF On. Other manufactures use different lanes but they all do the same thing. Once enacted, the AF On button allows the lens to focus on a particular point and remains there until it is pressed again.
- This eliminates the need to ever go to manual focus as the rear button acts as if the lens is being manually focused. Once pressed the focus point remains the same until pressed again.
- Rear button focus allows instant repositioning of the subject in the viewfinder with no loss in focus due to parallax shift. Especially when using wide apertures.
- Rear button focus allows for easy use of continuous focus tracking by allowing that setting to be permanently chosen. Tracking happens by simply holding down the rear focus button.
With the Nikon System the menu selection for rear button focus is in the Custom Settings area. Select auto focus and look for autofocus activation. Select AF On only and rear button focus is enabled. See detail photos below.
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