Chamonix camera 45N-1 focusing error

[Renato Tonelli]

GPS - I am not feeling better but thank you for trying I'm going to do a little more research before I decide on which 5x7.

[GPS]

Would do the same in your shoes too...;-)

[europanorama]

"But this is all moot anyway if you just remove the fresnel, or place it between you and GG, or replace the stock fresnel with some other screen intensifier.
It's really not as big a deal as many people have made it out to be."

Yes it can be a very big deal if the camera designer designed the fresnel to be in front of the gg. If you just take the fresnel out and put it on top of the gg or just replace it with another behind the gg or just throw the fresnel away you will probably need the ground position of the gg adjusted as it expected a spacer the thickness of the original fresnel lens.

i like people who read the ignorants the "leviten". Had the very same "problem" ignoring the diffraction problem (at 11/16)in newly designed lens in newest Horizon S3Pro and other versions. proved it, showed it in pbase until they removed the thread. its still in archive but no proofs/images. unsharp is unsharp no matter what is said. i can sing a song was busy during weeks with Dora Goodman Zone Z1-bodies(3 versions) and proved the two they produced(Light and 200series are not calibrated to infinity.

[europanorama]

I had posted this information a few months ago:

Quote:
Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?
I was a little baffled with this thread. Two people with the same camera having identical problems with a particular focal length lens. I would have thought that the Chamonix being a new camera the position of the gg/fresnel combination would have been tested. So I thought I would test my own Chamonix, and using mm ruler verify any small differences if they existed.

For a target I used a window mat on a mat board that would provide a bright line (reflecting the overhead light), and a dark line that would be a shadow from the overhead light. Both lines would be parallel to each other, and the target would also test flatness of the gg (i.e. there should be no change in focus of the parallel lines).

I checked three lenses, my 58mm Schneider XL, 90mm Linhof Scneider Angulon f5.6, and my Apo Sirornar S 135mm. All were tested with either the fresnel in the proper position, with it on top of gg, and no fresnel - just the Chamonix gg. I used a Scneider 6X loupe to check for focus.

With the 58mm lens the focal shift +0.5 mm with the fresnel in the proper place. With the 135mm lens the focal shift was +1 mm with the fresnel in the proper place. This should not make a big difference in depth of field unless shooting wide open I would think. However, with the 90mm lens the focal shift was +3.5mm with the fresnel in the proper place. There was no focal shift when the fresnel was placed on top of the gg. I have tried 2 other gg that I have, and made the same observation.

One possible explanation is the focal length of the fresnel is affecting the focus of 90mm lenses. I do not have another fresnel to test. But I think hereafter I will keep my fresnel on top.
End Quote:

I also followed up that I had put a Maxwell screen from another camera (that I had sold) on the Chamonix and saw no focus shift. I had a thicker cover glass so I cut shims (hose washers) for the gg hold-downs.

I honestly cannot see in any of my images that there is a focusing issue, but I generally stop down f22 or greater. I have had my camera almost two years. I think the only way this issue affects me is maybe where dof was critical and objects closest to me weren't as sharp as I may have thought - but that maybe operator error.

Mike

if the 90mm angulon has that much shift couldnt the smaller COC(if true) be the reason? smaller COC=shallow/less DOF= better resolution

[europanorama]

I just did some basic optical calculations and here are the numbers :

with a 150mm lens. when focused on a 5m away subject, a 1mm focus shift towards the user means a 86cm focus shift in the "object space"
and a 0.5 focus shift is a 47cm shift.

4m away subject, 1mm focus shift is a 56cm shift
and 0.5mm focus shift is a 30cm shift.

1. "5m away subject, a 1mm focus shift towards the user means a 86cm focus shift in the "object space"
meaning 5m minus 0.86m right?
2. can you give us the calculations how you got the other shifts also?
on Zone Z1 200series body is 0.84mm too short.resulting in focus-shift of 20cm at 3m towards shooter. 3m = 2.8m. 150mm lens.
is there a calculation rule? i could recheck that by comparing in Mamyia Universal Press/Super 23 cameras. lenses are in helicoids obviously.

[europanorama]

I just did some basic optical calculations and here are the numbers :

with a 150mm lens. when focused on a 5m away subject, a 1mm focus shift towards the user means a 86cm focus shift in the "object space"
and a 0.5 focus shift is a 47cm shift.

4m away subject, 1mm focus shift is a 56cm shift
and 0.5mm focus shift is a 30cm shift.

i will go the very same test with Sekor 150mm blue(razorsharp lens even fully open) of MUP/S23-system. its a the calibrated lens, was never off in my hands. only didnt have the values present when i repleid first.
i tested at 3 and 5m. shift stays at 0.84. shim-checked and verified. must dig out the values of 5m since i will not remove the shim or budy another body. Light version has a bit different shift. since i know that i will verify in real in this body too.