Mamiya RB67 mirror doesn't sit horizontally when raised

tih · Sep 10, 2015

I happened to exercise the shutter release mechanisms on my RB67 with the viewfinder off, and noticed something a bit worrying. When the mirror flips up, it seems not to raise the front right corner quite as far up as the others: that corner stops a few millimeters lower, not quite hitting the foam cushion. It sounds fine - no clicking sound of anything stopping it - and I guess it works just fine, since it's raised enough that it's fully out of the way of the light path, but it does look a bit wrong. When lowered, the mirror sits perfectly straight, as it should.

Should I be worried?

M Carter · Sep 10, 2015

If Paul Ron doesn't chime in here, (there was a url link here which no longer exists) - he knows the RB in & out.

flavio81 · Sep 10, 2015

tih said:
I happened to exercise the shutter release mechanisms on my RB67 with the viewfinder off, and noticed something a bit worrying. When the mirror flips up, it seems not to raise the front right corner quite as far up as the others: that corner stops a few millimeters lower, not quite hitting the foam cushion. It sounds fine - no clicking sound of anything stopping it - and I guess it works just fine, since it's raised enough that it's fully out of the way of the light path, but it does look a bit wrong. When lowered, the mirror sits perfectly straight, as it should.

Should I be worried?

Regardless of the top foam cushion, the mirror assembly has (or should have) foam along the borders of the mirror support. If they are worn, this could cause the problem you're experiencing.

It's never harmful to replace that foam -- and it is supposedly needed, because the mirror assembly acts as a light baffle so the light from the viewfinder does not enter the film after the exposure has been made.

StephenT · Sep 10, 2015

What flavio81 said.

tih · Sep 10, 2015

flavio81 said:
It's never harmful to replace that foam -- and it is supposedly needed, because the mirror assembly acts as a light baffle so the light from the viewfinder does not enter the film after the exposure has been made.

Ah, now I suddenly understand why there has to be a light baffle separate from the mirror itself: when you cock the shutter and mirror, the baffle comes down first, and only when it has closed the rear of the mirror box does the mirror start coming down, breaking its seal against the ground glass frame. When taking a picture, the mirror flips up first, and then the baffle follows, breaking its seal after the mirror has closed the top of the box. Neat!

There's plenty of bad foam elsewhere on this camera - I've just bought a bick pack of various foam types in order to fix just that - and I guess I should take a close look around the mirror box, too.

paul ron · Sep 10, 2015

The mirror doesnt sit perfectly flat. It has one edge lower than the other. DON'T try to straighten it or you will definately crack the mirror.

Your foam probably needs to be replaced anyway. The upper bumpers just under the view finder screen keep the mirror from bouncing. One side is double the thickness of the other. So just layer your thickest foam to make the difference. The sides of the mirror are seals n also serve as dampers. They get sticky n gum up the side ribbs n cause a delay when cocking so be sure to clean it off well with denatured alcohol. BTW DONT GET ALCOHOL ON THE MIRROR... it'll turn blue n ruin the silvering.

tih · Sep 10, 2015

Thanks, Paul! Good to know there's no mechanical damage. I'll inspect all the foam in the mirror box, too, and replace anything that's gotten sticky.

paul ron · Sep 10, 2015

While you're there jsut do it all. The bottom mirror bumpers n seals, the sides of the mirror, under the VF bumpers adn behind the baffle strip.

You know you'll never go back so why put it off once you're in gear?

Have fun.

tih · Sep 10, 2015

Yeah, I guess you're right. It just feels a bit scary, is all, working in close proximity to the mirror. I guess getting it out of harm's way first is more trouble than it's worth?

paul ron · Sep 10, 2015

no big deal... you'll be surprised how much room you've got. its like dental work... open wide n say ahhhhhhhhh.

if you're that uneasy... slap a postit on the mirror.

a puff of bad breath n a good cleaning when you're done will be very rewarding by morning.

M Carter · Sep 10, 2015

Duuuuude… get a Jon Goodman kit. Cheap, cut to perfect-fit size, quality foam, and very very detailed, step-by-step instructions with plenty of photos.

I did my RB and it took maybe an hour or so. Hardest part was getting the mirror foam completely off and clean. Google his name to get his contact info. Very very affordable, I think well under twenty bucks for mirror foam and all light sealing foam. And fairly immense satisfaction factor when completed.

flavio81 · Sep 10, 2015

paul ron said:
The mirror doesnt sit perfectly flat. It has one edge lower than the other.

Wow, didn't know that. Any idea why the design is like this?

paul ron said:
if you're that uneasy... slap a postit on the mirror.

Interesting tip.
I'm assuming that the glue of the post-it will not stick to the mirror, of course.

Anyway, thanks Paul! I learn more about my favorite camera.

paul ron · Sep 10, 2015

the only thing ive ever seen about the mirror is a small blurb in the repair manual. it says to maintain mirror parrallell, the left corner of the mirror holder is offset by 3mm.

anyone want to explain it? beats me.

Mikkornat · Jul 6, 2016

tih said:
I happened to exercise the shutter release mechanisms on my RB67 with the viewfinder off, and noticed something a bit worrying. When the mirror flips up, it seems not to raise the front right corner quite as far up as the others: that corner stops a few millimeters lower, not quite hitting the foam cushion. It sounds fine - no clicking sound of anything stopping it - and I guess it works just fine, since it's raised enough that it's fully out of the way of the light path, but it does look a bit wrong. When lowered, the mirror sits perfectly straight, as it should.

Should I be worried?

I noticed the same thing with my RB67, and so I came here to see if it was a problem or not. According to this thread it's not. I was concerned that it would affect focusing. But it seems that the mirror is flat when it's lowered. It's just slightly tilted when it's up.

Mamiya RB67 mirror doesn't sit horizontally when raised

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