Procedure for replacing the ground glass? Ensuring the correct plane of focus registr

[l2oBiN]

A while back I have taken the gg of my arca Swiss camera to clean off dust that was stuck in between gig and fresnel. To my horror, after I started washing the gg the reference lines washed away too! It seemed that they are only some sort of string..

Now, I have printed a pattern on a transparency and overplayed on top of gg for reference, but I would like to get my reference lines back without the transparency.

Further, my Wista gg seems much brighter than arca. This got me thinking of replacing the arca gig with a better alternative .. Any suggestions?

So if I was to take a different gg what would be the procedure for installation and ensuring correct registration?

[Jac@stafford.net]

It works to pencil guide lines on the rough side of the GG. Regarding replacement of the glass, get a GG with the same thickness. If there were shims over the GG, be sure to replace them. That point frustrated me once when they fell out before I could see exactly where they were. :(

[l2oBiN]

Let's say I had different thickness glass... What is the procedure for registering the image forming plane?

[cowanw]

Actually if the ground side is on the lens side, as is common, the thickness of the glass is of no concern with regard to focussing.

[Jac@stafford.net]

Actually if the ground side is on the lens side, as is common, the thickness of the glass is of no concern with regard to focussing.

I stand corrected. Thank you.

[Emmanuel BIGLER]

So if I was to take a different gg what would be the procedure for installation and ensuring correct registration?

Hello from France.

To the best of my knowledge, below is listed is the correct order and orientation of surfaces found in the Fresnel + GG combination on my Arca Swiss camera, coming from the lens side and going to the operator's side.

- flat side of the Fresnel
- corrugated side of the Fresnel
- frosted side of the GG
- polished side of the GG.

The image is focused through the Fresnel lens on the frosted side of the GG. Hence there is a certain optical path through the Fresnel thickness which is precisely compensated by the design of the back.

I do not know which model of Arca Swiss camera you have, but if you re-mount the various Fresnel + GG surfaces in the right order as previously described, bringing back the system to its original arrangement, of course you keep the proper registration.

I you want to replace the original A/S GG by something else, if the 3-rd party GG has exactly the same thickness as the original, no problem, you keep the proper registration and sharpness.

However if your 3-rd party GG does not have the same thickness, you should look and see how and where the assembly is held against the metal frames of the back, in principle you should know since you already have disassembled the combo.
Look to check if changing the thickness in the 3-rd party GG would modify the position of the frosted side of the GG with respect to the reference plane where the film holder seats.
If the frosted side of the GG does not move, it is OK. If the frosted side of the GG changes place because of different glass thickness, you have to find something to mechanically compensate for this.

Good luck !

[l2oBiN]

Is the image formed on the ouer plane of the ground glass, hence the thickness should not matter?

[cowanw]

The image is formed on the ground surface.
If the ground surface is on lens side, thickness is not issue as long as the glass physically fits.

[l2oBiN]

Sorry cowanw, I am a bit confused here...

[cowanw]

The image is formed on the ground surface of the ground glass. If the ground glass is placed With the Ground side on the side away from your eye, but on the side closest to the lens, on your original setup, then any thickness that fits will be correct if the GG is placed similarly, ground side on the lens side. This is most common be not invariable.
If there was a Fresnel next to the ground surface on the lens side then use the same setup as it came to you.
If your original setup had the ground surface on the side of the glass closest to your eye and on the side farthest from the lens, then the thickness of the glass is significant. The Fresnel must be in the same place as original.
The ground surface must be in the same distance from the lens as original.

The key is the ground surface must stay the same distance from the lens.

Describe your setup.
Is it smooth as glass on the back side; is the ground surface on the inside
Is the Fresnel and Gg one piece or two pieces
If two piece Fresnel, is it on the lens side or the eye side of the ground glass