With the 85mm I get about 2.5 revolutions on my redrock v2 follow focus so I thought, maybe I can actually use the witness marks on this SLR lens if I found the film plane on the 7D? I measured from a point near the hot shoe of the camera as an approximate starting location of the film plane to an object 4 feet away-I was pretty close to the actual film plane, I didn't spend time to find the exact mark. But then I measure from the same point to an object eight feet away and set my lens to 8 feet but the picture is completely out of focus?! I have to set the focus on the witness marks to a much shorter (maybe 6ft?) distance to get an object 8 feet away in focus. Effectively I found the film plane would be in front of the lens according to this camera's witness marks? What's going on here?! Any idea why the film plane would shift? I realize the witness marks on SLR lenses aren't exactly perfect but something seems to be wrong here...the film plane is shifting forward a foot or so?
Edited by Salil Sundresh, 14 May 2010 - 06:08 PM.