Originally Posted by

**Len Robertson**
Here is a formula I got years ago from the late Jim Lipari, a great Cirkut repairman and friend of Cirkuts.

(Constant) divided by (Number of Teeth of Pinion Gear) equals (Distance Of Nodal Point of Lens to Film Plane) For your #6 Outfit (assuming you have to correct 9 1/16" diameter gear head) the Constant is 438.46 inches or 11136.88 mm. I believe the concept of lens nodal point has been covered on this forum, or you can do a search for information. The important point is, as the lens focuses closer from Infinity focus, the Distance of Nodal Point becomes greater, and the number of teeth of the pinion gear changes.

However, if you actually want to shoot with your Cirkut, I would very much advise you ignore all this. Whoever put together the Outfit you have seems to have done all the calculations already. I think what you need to do is set up the camera body on a tripod with the focusing back on and make a focusing scale to match the gears you have. I would just make a scale for the 7 1/2" focal length, in order to simplify things. Focus the lens to the distance in feet for each gear and make a mark in your scale with the gear number - Infinity 60 gear, 28' 57 gear, etc. I would start with just one scale for the 7 1/2" lens and try shooting with it and see if it works for you. Forget all the other gears and focal lengths for now.

Len