”  I find it difficult when I

"  I find it difficult when I'm changing the focus in a shot because it's hard to tell when I need to stop focusing "         The BIG BOYS use a dial apparatus added to the focus ring on the lense AND there's an assistant to operate it. In many cases, the beginning and the end of a rack focus is determined by actual measurements from the subjects to the focal plane of the camera.  Digital video camera's LCD screens or eye-piece monitors are so woefully lacking in detail one MUST use a large external HiRes monitor in order to visually determine optimum focus.