Mamiya 645 infinity focus adjustment

[REAndy]

Does anyone have any ideas why 2 Mamiya 645 bodies would focus at infinity (with the same lens) differently? And any ideas how to correct it?

I don't know if the lens to viewer distance from one body to the other is the only thing different or not. It is possible that with "bad" body and lens at infinity, film will be in sharp focus (i.e. only lens to viewer distance is bad; lens to film plane is good). Nothing visually obvious looking down into the camera body (mirror, lens mounting hardware, etc.)
(Note: I have not yet ran a roll of film thru the "bad" body at infinity for testing purposes, but plan to soon.

More details: On one body, with my 80mm and 45mm lens, they focus perfect with the lens set at infinity, and viewing something far away. On the other body, same lenses set at infinity, and viewing the same distant object. It's out of focus beyond infinity, I have to "focus the lens back a bit" to get infinity distance into focus.

Swapping viewers (prism and waist-level) makes no difference.

To summarize: any lens and any viewer on camera body A, infinity focus good. any lens and any viewer on camera body B, infinity focus is bad.

 

[shutterfinger]

There are several versions of Mamiya 645, the 645 Pro instruction manual shows on page 24 that there are 4 additional focusing screens available for the camera and that instructions for changing them come with the screen.
http://www.cameramanuals.org/mamiya_pdf/mamiya_645_pro.pdf
A repair manual for this camera is available for download at http://www.suaudeau.eu/memo/Manuels/Mamiya_M645_Service_Manual.pdf
1st I would compare the focus screen installation in both cameras, if a difference is found change the suspect bad camera match the known good.
2nd. verify that the reflex mirror is returning to the correct position, again comparing suspect bad body to known good body.
3rd with the shutter locked open on B place a temporary ground glass at the film plane and verify that the lens distance scale matches the focused distance on the ground glass, use a loupe to check the focus.
A temporary ground glass can be made by placing strips of Scotch Magic Transparent Tape next to each other on a piece of glass or clear acrylic/plastic. The tape side faces the lens.

Edit: On page 31 (PDF 29) of the service manual it states that the mirror should be at 45° in the down position.
On page 55 (PDF 53) is a diagram that shows the focus screen with the curved side up toward the finder, the bayonet (lens mount) to both the inner and outer film rail distances, should be easy to measure.

 

[REAndy]

shutterfinger: Thanks for the info and the links to the manuals! I will try swapping the focus screen (1st on your list). I did check to see if the focus screen could have been put in upside down on the bad one, but the "tab/handle" on the focus screen fits into a slot, so it can only be inserted in 1 direction. But I didn't think to swap them.

#3 is also a great idea, I can do that too.

#2 would be suspect if I ran a roll of film thru, and snapped picts of "infinity distance" objects and get sharp/in-focus negs. But I will check with the shutter open (mirror up) and see if I can see the "stops" the mirror rests on in the down position, and see if they seem normal/mis-aligned/bent.

Great ideas for me to try, and thanks again!
REAndy

 

[Neil Grant]

..which version of the Mamiya 645 do you have? On the orginal, all metal version, the focusing screen sits on three user-adjustable cross head screws. Of course the mirror must be at 45 degrees when 'down'. There's a spring loaded stop in the mirror box for this but i guess it could go out of adjustment.

 

[REAndy]

Neil: one body is a 645 Pro, the other is a 645 Super. I will check to see if this model also has those focusing screen adjustable cross head screws.
Thanks for the tip.

 

[MattKing]

You need to take some photographs with both bodies.
There may be nothing disastrously wrong with either body or lens. The lens mount on one camera may just be slightly farther away from the film plane and mirror than it is on the other camera.
It may turn out that the in-focus plane in your photographs matches the in-focus plane in the viewing system of each camera. In that case, the only function that would be affected is scale focusing - focusing based on the distance indicators on the lenses. That and a marginal difference in the close focusing capabilities of the cameras.

 

[lobitar]

Don't want to appear condescending, but it would have been nice if you had attached pictures of your cameras in the first place, as of the four models of the 645 that I know of the 3 are totally different. As it's the model Pro and Super you have, I regret to say that I think you are 'sunk' as for the sample with problems. Sounds to me as it's very likely an issue of adjustment of the mirror-angle, that's a problem I have seen repeatedly with these models. And sadly for me they have been well-nigh impossible to adjust in this respect, as the fittings for the adjustment-screw - as well as the screw itself and its nut - are fabricated of cheap plastic that simply turns to dust when you touch it. As said, I've seen this repeatedly. I can say for sure, I'll never own either of these 'plastic' cameras again. But best of luck - hope you manage one way or another

Edit: Come to think of it, I believe all 4 specimens of these cameras I've had were the Super-model. The first worked ok, but the next 3 all had the mirror-angle calibration problem. But the problem may not apply to the Pro-model!

 

[John Koehrer]

First things first.
Shutterfingers suggestion #3 would be the first thing I'd check. It's the simplest and most people have
some tape around the house. Some lenses will focus slightly beyond infinity and it's pretty common.