You should read this thread
Hello! I'm restoring my Linhof Technika III ver. 5 which did not have a fresnel lens when I got it. It doesn't seem to be designed to take one, as putting both a GG and a fresnel in the little compartment area gives literally no room to adjust the focus position, and that doesn't seem like...
www.photrio.com
There’s not much information on the internet about your question and no consensus so I can’t help much.
Some people say the fresnel is meant to be installed from the manufacturer on the lens side of the ground glass with the grooves facing the ground glass and that if you remove it you must place shims between the ground glass and the lens to maintain the T-distance.
Others say that if your ground glass is already in the correct orientation it might be better to place the fresnel behind the ground glass, away from the lens with the grooves facing the ground glass. This will preserve the T-distance but the fresnel will be in a more vulnerable place and you will have to be more careful not to scratch it. This is however the way that fresnels are meant to be installed on the majority of cameras so it can’t be that bad.
You could try removing your ground glass very carefully and looking for shims. If you find shims between the back and the glass you could measure them and compare that to your fresnel, install the fresnel and shim accordingly. Assuming your fresnel is thinner than the depth of the shims.
If there are no shims then you would have to place the fresnel on the side of the ground glass that faces away from the lens with the grooves facing the ground glass. This assumes that the T-distance on your camera is set correctly as there is a chance that the shims should be there even though they aren’t. You can tell if your t-distance is off by testing it. If the shims are needed and missing the photos your camera produces will be focused slightly closer than you set it based on the image on the ground glass.
Finally I saw a very good suggestion on another forum which was to call linhof and ask them what you should do. If you do that please post your results here as it would be valuable information for other users in the future.
