I知 looking to reconcile two contradictory findings in my pseudo-scientific endeavor to nail down focus on the BOSSCREEN ground glass that my camera came with.

I知 presenting my method and if someone can spot my mistake I would be very grateful.

I was shooting slides (E100G) for the first time and was just a little disappointed with the detail on the horizon of a landscape scene. The shot was made racked against the infinity stop of a Linhof Tech V. Now, I have checked the infinity stop against the GG painstakingly in my endeavor of projecting a laser through the rangefinder. My new paranoid hunch was that maybe the GG was not co-registered with the film plane. Now, the previous owner cannot be asked how he installed it, because he fell victim to cancer (which is why I have the camera).

Since I had a big load of old Xray film I commenced to photograph a table top with a newspaper on it at 45ｰ



I focussed on a particular line (thin line under "Asset Management" at 10cm on the paper ruler) but the focus on the developed sheet seemed to be 1 cm out.

Now, 3 columns of text were (roughly) 18cm wide on the paper and 7cm on the film giving a magnification of 1/2.6. The other calc 150/(545-150) found the same ratio of 2.6.

I calculated with 10mm offset "(10mm * (sqrt(2)/2)) / (2.6**2) = 1mm", and hence got 1mm film deviance from the ground glass.



Also in the repeat.



Then I lifted the BOSSCREEN from its frame and found no metal shims (which are supposed to be there on a Technika) but two 0.9mm thick rubber-like stacks of electrical tape instead of shims.