Focusing error with split image screen

I've encountered an annoying phenomena with my Exaktas.

There's namely a focusing discrepancy between split image screen and

every other screen I tested when using lenses of focal length other

than 50mm.

Have you got any experience with something similar?

 

Best regards,

 

Miha

Is the screen in upside down? The 1 mm or so difference due to the thickness of the glass could cause a very noticeable focusing discrepancy...

The screen, when used, is mounted properly in either a prism or a waist level finder. Also, it works properly with a 50mm lens...

 

Thank you,

 

Miha

Here in the USA I once used a VX ; a VX1000; and a VX500. I had microprism and spilt screens. The bodies here mostly used with Pancolar 5cm F2; Domiplan F2.8 Vivitar 135mm F2.8; 135mm F4.5 Steinheil Culminar; Kodak Ektar 178mm F2.5; and a telescope of 1220mm F8. The VX500 body was the newest; and had a film plane not parallel with the lens flange. This gave screwed up focusing results. The split image screens need a faster lens. Which Exakta camera body do you have and what lens?

There'd been a focusing issue with one of my Varex IIbs and it had a mirror adjustment done. To check whether the repair was done well, I took few pictures of a slanted ruler with CZJ Biotar 1,5/7,5cm (the fastest lens I own) at f/1.5 and 1:1 magnification. There was approximately 1mm back focus. The pictures were taken using a split image focusing screen.

Before taking the body back to repair shop, I did another quick test, just to be sure, using different finders, but everything else being equal. To my surprise, there was an obvious difference in focusing point between split image focusing screen on one side and plain ground glass and microprism screen on the other side.

 

On Sunday, when there was enough time, I tested more extensively with three Exakta Varex IIb bodies, 2 waist level finders, Ihagee Version 5 and 6 prisms, Examat prism and Travemat prism (this one only with its proprietary screen). The screens used were 2 ground glass ones, 3 Ihagee microprism ones, Examat microprism one and a Travemat miroprism screen (used only with the Travemat finder) and of course Ihagee split image fresnel screen. The results were the same regardeles of body and/or finder used. As a target I used same slanted ruler and testing was again done in approximately 1:1 magnification range, to reduce depth of field.

 

Split image screen works well only with a 50mm lens. Even using it with a 58mm one results in a back focus situation.

 

The lenses were Meyer G�rlitz Lyidith 3,5/30, CZJ Flektogon 2,8/35, CZJ Tessar 2,8/50, CZJ Pancolar 2/50, CZJ Biotar 2/58, CZJ Biotar 1,5/7,5cm, CZJ Biometar 2,8/80 and Meyer G�rlitz Orestor 2,8/100.

 

 

Later, I did a test under much different condition (5m to target) with a Sonnar 4/300 and found the same back focus issue with split image screen.