Wista Ground Glass Sandwich Question

[shutterbug guy]

Doremus Scudder,

I'll know for sure what the orientation will be once I take delivery of the ground glass pair. From what I can see the glass is nothing more than a protective cover for the fresnel screen, the screen being the focusing aid. As long as the focusing aid is on the true focus plane one shouldn't have any issues. I've noticed on one YouTube video https://www.youtube.com/watch?v=CVpveOEk-I0&t=513s that this guy apparently has a combination where both the ground glass and the fresnel screen were the focusing aids hence his need to install both of them from opposite sides of the holder allowing each to share the same focus plane. That's something I don't want to do.

It sounds like you are right with the Wista ground glass combination. I wouldn't know as I haven't seen one.

[Doremus Scudder]

shutterbug guy,

By "focus aid" I assume you mean the focusing surface, i.e., the frosted surface of the ground glass (or acrylic or whatever) upon which the image is formed. So, you're correct that this surface needs to be in alignment with the film plane.

The only real problem with focus and Fresnel screens is the one I described. If your camera was originally designed for a regular ground glass, then when adding a Fresnel screen, it needs to be positioned between ground glass and photographer so that the focusing surface remains at the same place as the film plane.

There were (are still?) some cameras that came with a factory-installed Fresnel screen that was placed between the frosted focusing surface of the ground glass and the lens. Placing the Fresnel this way causes a focus shift, so the position of the focusing surface (the frosted surface of the ground glass) had to be positioned differently than the film plane. Replacing such an OEM sandwich with a regular ground glass throws the focus off. Shims are needed to get focus correct.

Best,

Doremus