Mamiya RB67 SD - on screen focusing issue

[Deleted member 88956]

I have just noticed that one of focusing screens does not seem to behave properly. It is a plain one with center spot, no split image or microprism. Once focused it does not show crisp lines of a subject but rather a double line with one being faint yet quite visible. Almost like if one had a vision problem or ther was a separation within screen. Since I have to 2 SD bodies and several lenses, I ran a swap test with several combinations, so the culprit is in the screen.

Screen itself is actually in near new condition and there is nothing visible on it to suggest registration problems. And it is original Mamiya screen too.

Any ideas what the problem is?

 

[shutterfinger]

Any ideas what the problem is?

The reflex mirror or alignment of the mirror and focus screen.

 

[Deleted member 88956]

The reflex mirror or alignment of the mirror and focus screen.

I have already tested the body with different screen, it is not the body or mirror. Screen is the difference. If I'm careful looking at the right detail I can get it to focus properly, but the second fainter line makes result suspect, so I will not be using this screen until I figure out why it is doing it.

 

[shutterfinger]

The second faint line is a reflection/ refraction through the screen. Mirror alignment to the focus screen is off 1/4 second of arc or less. Have you checked the thickness of the focus screen across the screen with a caliper? Does the screen sit into the mount perfectly?
A .0001 millimeter shift can cause such an error. The focus screen may be defective.

 

[Deleted member 88956]

The second faint line is a reflection/ refraction through the screen. Mirror alignment to the focus screen is off 1/4 second of arc or less. Have you checked the thickness of the focus screen across the screen with a caliper? Does the screen sit into the mount perfectly?
A .0001 millimeter shift can cause such an error. The focus screen may be defective.

I've not done any measurements yet and yes, I am suspecting screen having some issue, even if it does not look used much, including the frame. Perhaps i got a lemon. It did come with one of SD bodies, but never noticed it until first - some more critical focusing, which then I started seeing rather easily no matter how I looked through it or at what. Just annoying. Good thing I swapped screens before calling an eye doctor.

 

[shutterfinger]

45 years ago I set up a guidance system for calibration using a theodolite and mirror 100 feet away. The theodolite projected a reticle onto the mirror which reflected it back to the theodolite. Similar is used today to align lasers.

is as close to the one I used as I can find. Printing two of these on transparency material, attaching one to each side of the screen ensuring perfect physical alignment should show any optical error of the screen.

 

[Deleted member 88956]

45 years ago I set up a guidance system for calibration using a theodolite and mirror 100 feet away. The theodolite projected a reticle onto the mirror which reflected it back to the theodolite. Similar is used today to align lasers.
View attachment 256040 is as close to the one I used as I can find. Printing two of these on transparency material, attaching one to each side of the screen ensuring perfect physical alignment should show any optical error of the screen.

Thanks for this, but I don't think I'm going to attach anything to the fresnel side of screen. While it might help finding the problem, it might also rather likely blemish the screen.