Mamiya RB67 Pro S Focusing Issue

digicam10 · Apr 29, 2020

Hi all, I have an rb67 that has a focussing issue. It appears to be back focussing, I’ve taken it in to a local repairman who said he calibrated the focusing screen but the issue is still there. Is it possible it could be a mirror issue and if so how do I go about fixing it?

I replaced the foam underneath the mirror myself but I can’t see how it effects how the mirror sits (I’ve lifted it up and its still metal resting on the fabric cover that comes down first, is that correct?)

shutterfinger · Apr 30, 2020

Download the repair manual: https://www.manualagent.com/mamiya/rb67-pro-s/repair-manual

Optical distance from lens to film plane muse be the same as the optical distance to the view screen. If you replaced the mirror foam the mirror must rest at the same position as it did from the factory.

Mamiya_Repair · Apr 30, 2020

Adjusting the focus on the RB67 means having the focus screen and the film plane both in focus. This is done by adjusting four screws under the focus screen. If your technician did adjust focus and you are still having an issue, first thing I would check is the rollers at the film plane in the film back. The roller supports often break and cause focus problems. If this is not the problem, you can do a quick check by taking out the film insert and putting a ground glass on the focus rails of the back (OK, technically the point of focus in a PRO S back is actually .1mm behind the film rails, but this is close enough for this test). Put the lens on T, release the shutter and focus on an object from 1-3 meters until the image is sharp. After taking the shutter off T setting, cock the camera body and the image in the viewfinder should also be in focus. If it does not coincide, it would not be unreasonable to return the camera to your repair shop for further inspection.

digicam10 · Apr 30, 2020

shutterfinger said:
Download the repair manual: https://www.manualagent.com/mamiya/rb67-pro-s/repair-manual

Optical distance from lens to film plane muse be the same as the optical distance to the view screen. If you replaced the mirror foam the mirror must rest at the same position as it did from the factory.

I cant manage to find a photo of how the mirror should be sitting online at all, the mirror cant be pushed down any further (its resting on the little metal stoppers on the sides of the camera). Does the light seal foam need to runner over the little studs on the underside of the mirror or stop just before them?

shutterfinger · Apr 30, 2020

Page 26 step 7 - mirror holder shall touch stopper of both sides of the body.
Too many years since I owned a RB. The light seal should keep light from the finder from entering the image path when the mirror is up therefore the foam should be on the top of the mirror frame and not interfere with the mirror holder touching the body stops.

digicam10 · Apr 30, 2020

Ok well by the looks of the manual the mirror is sitting correctly, I have a roll in at the moment so will finish that off and check the rollers in the film back but I’m fairly certain they’re are fine also. Such a weird problem that I cant narrow down

digicam10 · May 1, 2020

Mamiya_Repair said:
Adjusting the focus on the RB67 means having the focus screen and the film plane both in focus. This is done by adjusting four screws under the focus screen. If your technician did adjust focus and you are still having an issue, first thing I would check is the rollers at the film plane in the film back. The roller supports often break and cause focus problems. If this is not the problem, you can do a quick check by taking out the film insert and putting a ground glass on the focus rails of the back (OK, technically the point of focus in a PRO S back is actually .1mm behind the film rails, but this is close enough for this test). Put the lens on T, release the shutter and focus on an object from 1-3 meters until the image is sharp. After taking the shutter off T setting, cock the camera body and the image in the viewfinder should also be in focus. If it does not coincide, it would not be unreasonable to return the camera to your repair shop for further inspection.

Ok so I had a look at the rollers and none are bent or broken. I’m not home at the moment so dont have a spare ground glass or tripod with me to run that test, when I have done previously it was off though.

John Koehrer · May 1, 2020

Was there a difference in thickness of the foam? Because the frame is right doesn't mean the mirror isn't too high.

digicam10 · May 1, 2020

John Koehrer said:
Was there a difference in thickness of the foam? Because the frame is right doesn't mean the mirror isn't too high.

The foam at the bottom of the mirror is 2mm thick

John Koehrer · May 2, 2020

Was the original also 2mm?

digicam10 · May 2, 2020

When I replaced it the previous foam had completely deteriorated so wasn’t anything to compare to, I just went off a video I watched stating 2mm

shutterfinger · May 2, 2020

I just looked at a you---- video and the foam only goes around the edges of the mirror and seals the mirror frame to view finder opening during exposure to prevent light from the viewfinder from entering the image box.
If the mirror is flush to the mirror frame, the frame is touching the body stops, and the front edge is flush to the bottom of the opening then the mirror is not causing the focus problem.

In post 3 a description of focus testing is given using a close target. Such a target must be parallel to the film plane and the distance measured to the film plane. I prefer to use an infinity target that is at least 1524 meters (5000 feet) away. 1 mile=5280 feet= 1.6 kilometers. Celestial objects make excellent infinity targets.
The film holder should have two sets of guides, the outer one for the backing paper, the inner one for the film. Fit a ground glass to the film guides and then focus the target with a loupe. Now check the focus of the viewfinder with the same loupe. Adjust the view screen to match the film plane.

A piece of plain glass with transparent tape strips placed next to one another without overlapping makes an adequate ground glass. Place tape side facing the lens.

digicam10 · May 6, 2020

Shutterfinger,
After doing some experimenting it appears that using the moon as my target, it looks possibly just out of focus. Thats with the baffles fully retracted at infinity, focusing closer makes it further out of focus. Does this align with my current thought of it back focusing?

shutterfinger · May 6, 2020

If you are unable to focus infinity at the film plane the bellows rails are off a tooth or two of the focus mechanics of the camera. Look at the bottom of the bellows rails to see the teeth that the pinion rod the focus knob attaches to engages with.
It jumped a tooth or two due to force or wear. Check the repair manual linked to in post #2 for instructions on accessing and adjusting/setting up the pinon and bellows track.

digicam10 · May 6, 2020

Before I go head first into taking it apart, is this an easy-ish job to perform? I can't find any videos or clearer instructions on how to go about it so I'm a little hesitant to jump straight in

shutterfinger · May 6, 2020

Can you post a picture of where you are putting the focus plane test ground glass?
Remove the bottom cover of the camera body, just a few screws then the cover plate lifts up and off. Inspect the focus rails and pinion and post a picture of them.

flavio81 · Jul 13, 2020

digicam10 said:
Hi all, I have an rb67 that has a focussing issue. It appears to be back focussing, I’ve taken it in to a local repairman who said he calibrated the focusing screen but the issue is still there. Is it possible it could be a mirror issue and if so how do I go about fixing it?

I replaced the foam underneath the mirror myself but I can’t see how it effects how the mirror sits (I’ve lifted it up and its still metal resting on the fabric cover that comes down first, is that correct?)

Sorry but what you have is a faulty repairman.

Those four pins under the focusing screen are for calibration but should better be left alone since I can't imagine what would mess with the focusing.

Mirror angle and proper mirror seat position should be confirmed before anything else.

I'm assuming camera wasn't hit and thus some bellows alignment was distorted.

artyfarty · Aug 13, 2023

I've bought a very cheap RB67 Pro S and it required some tinkering. I've also encountered terrible focusing issue. It was clear that it's not a focusing screen issue, because i had to tilt it up half a centimeter from it's resting place. It was the mirror not going all the way down.
This problem is not covered in service manual. It was mirror return spring RS2457, that should be routed around a small white plastic roller to actually pull the mirror down, not sideways. Turned out it somehow jumped out of there. Simply routing it back with a pair of tweezers fixed the issue.

Donald Qualls · Aug 14, 2023

artyfarty said:
Simply routing it back with a pair of tweezers fixed the issue.

Always nice when it doesn't need (hard to get) parts...

Mamiya RB67 Pro S Focusing Issue

Attachments

Privacy & Transparency

Privacy & Transparency