No need to measure. I just refurbished my Isolette and reset the infinity after cleaning out the lense.
- Open up the camera and lock the front standard into position.
- Screw the front cell of the lense all the way in.
- tape wax paper, frosted glass, frosted plastic, scotch tape at the film plane to serve as a ground glass.
- focus on something very far away by slowly unscrewing the front cell out
- when in focus, thats infinity.
- you can rotate the outer marked ring to the infinity mark and lock it down with the 3 retaining screws
- if your camera has a rangefinder, calibrate the rangefinder to the new infinity
Option 2: (I think its easier for these rangefinder type cameras)
- use the lense coliminating method to set infinity by using another camera
- I used my Hassy with an 80mm set at infinity
- You'll position the 2 cameras facing each other about an inch apart
- set up your rangefinder camera per the first 3 steps above
- tape a bunch of black hair on your ground glass surface or mark it with a thin marker (at the film plane surface)
- shine a strong light through the ground glass towards the lense.
- Sight through the Hassey viewfinder and rotate the lense on the rangefinder until your hair or penlines are in focus
- Infinity found - now lock in the position per above.
Hope that helps, Bharat