It is a learned skill but one that can be immensely helpful when you are trying to capture action happening outside of the immediate viewfinder…

This skill takes some time to learn but is very helpful for operating any kind of camera. Try keeping both eyes open while shooting. It takes time to learn and has to be practiced consciously. Normally we close one eye and look through the viewfinder with the other. It is almost impossible to concentrate on two different images, but we can shift our concentration from eye to eye, what the camera sees to what our unaided eye sees. This is very helpful for watching when something is about to enter our picture that we want or do not want to include in our frame. Or we might be watching for a bottle, tomato or hand grenade coming our way. To learn this skill we merely shift concentration from our pocket viewfinder or camera back and forth to what our unaided eye sees. Pointing the pocket viewfinder or camera to one side helps for this exercise. Don’t blink, just shift your concentration.

~ Ron Dexter