Mamiya 50mm f/4.5 (RB67 ) - Elements interchangeable?

[Kirks518]

I have 2 Mamiya Sekor 50mm f/4.5 lenses. They are the old version, not the C or any other letter designation.

One has a messed up shutter and aperture (loose shutter blades, oily aperture, etc.), but has near mint glass.
The other has a fine shutter and aperture, but the elements have enough scratches to compete with ground glass.

Would I be able to swap out the elements between the two lenses and still have proper focusing? My concern is the front element set because of the floating element(s).

 

[Xmas]

I'd try fixing the shutter and iris first.
It is not unknown that glass is not interchangeable.
If the moving parts are kaput swap them.
note we are having problems stripping the c 50mm please take photos.

 

[shutterfinger]

Swap all lens components from one to the other including shims, housings. I did similar with 127mm lens of slightly different vintages years ago. In other words strip the good shutter down to the shutter and swap all the stuff from the bad one over to it.

 

[Kirks518]

Xmas, that's what I tried to do, but man there are a lot of springs and ball bearings in there! I made things worse on the non-functioning lens, and I now have extra screws from that lens. Unfortunately, I can't find a parts diagram or repair manual for the lens to help me put everything back in place....

shutterfinger, when I took apart the bad lens, the only shims I found were on the back side of the shutter assembly. They weren't near a lens group. The front groups are all housed in a single plastic mount, not including the control and trim rings. Would I just have to move the single plastic mount? The group screws into that mount like it was a helicoil (is that the right word?).

 

[EdSawyer]

Mamiya (MAC) supplied me with parts and service diagrams for the RZ lenses I have worked on. There have to be parts diagrams for the RB ones also.

Did the RB 50mm have a floating element? I had thought only the RZ 50mm ULD had that.

You should be able to swap the optical cells over and have it all work ok. I have done similar things on RZ lenses.

 

[M Carter]

I believe the non-C doesn't have a floating element. Some people get confused by the DOF ring.

I don't think you even have to strip it down too far to just swap the elements. RB fronts usually screw out once the name-ring is removed, though it may be easier to remove the metal surround (three screws on most lenses); the rear may just come out with a spanner wrench. This varies from lens to lens, but I just cleaned a 65 and had both groups out in about a minute. Swapping 65 elements would have taken about 2 minutes.

To get the name ring off, I use a "fernco" plumbing adapter, they have one that's the perfect size, available at any hardware store for a couple bucks.

 

[shutterfinger]

You should be able to swap the plastic barrel with lens elements in it and the rear element with no further disassembly.
Mamiya uses Seiko Shutters.

 

[flavio81]

I believe the non-C doesn't have a floating element. Some people get confused by the DOF ring.

I did not know that a 50mm "non-C" lens existed. And i'm something of a RB67 "nerd".

I suspect that if a 50/4.5 "non-C" lens exist, it also has the floating element design.

To the OP: If i were you, i would only swap the front (scratched) element and then test the resulting lens with film for sharpness.

Otherwise i'd try to swap the good shutter into the good lens.

 

[Kirks518]

I did not know that a 50mm "non-C" lens existed. And i'm something of a RB67 "nerd".

I suspect that if a 50/4.5 "non-C" lens exist, it also has the floating element design.

Yup, and yup.

These are crappy cell phone pics of my 3 50mm's; C, and 2 non-C

 

[Kirks518]

You can easily the different coating on the C lens, the C also has an improved PC socket, and a different baffle (?) at the rear of the lens.

 

[flavio81]

Yup, and yup.

These are crappy cell phone pics of my 3 50mm's; C, and 2 non-C

Wow...

I like the 50/4.5 lenses, but it seems you like them too much!!

The difference in coatings is visible. But does the "C" version really looks better through the viewfinder?
Also, the non-C lenses seem to have different coatings, or is this due to the angle?

Those are great lenses. Low in distortion, and sharp. Mamiya knew what they were doing.

 

[Kirks518]

Not sure on the 2 non-C's. I didn't notice that, but I'll check later and let you know.

It's not that I like them so much (i do like them tho), it's just I got a deal on a box of RB stuff. The C and one of the non-C's were in the box, along with a 90mm, a motor back, and a 220 back. And some other assorted stuff.