Mamiya RB67 Sekor C 65mm f4.5

MichaelMcC · Jul 10, 2024

Hi all,

This lens has what I am guessing is separation but I have never seen it look like this.
Not the end of the world as it doesn't seem to show up in shots and everything is really sharp.

Just curious about it and thought I'd see what you guys think.

Cheers

zoo · Jul 11, 2024

It is hard to tell from your images but it might be oil or some kind of optical fluid between elements 2-3 or 7-8, which are both locations where convex optics are directly or nearly directly in contact, and where the elements have either drifted apart so that surface tension no longer works as designed, or the fluid has begun to evaporate or polymerize.

The term for this is "oiled doublet" and should be an easy repair.

If you are satisfied with the quality of your images, don't bother. But it could be the cause of reduced sharpness or other defects.

MichaelMcC · Jul 12, 2024

zoo said:
It is hard to tell from your images but it might be oil or some kind of optical fluid between elements 2-3 or 7-8, which are both locations where convex optics are directly or nearly directly in contact, and where the elements have either drifted apart so that surface tension no longer works as designed, or the fluid has begun to evaporate or polymerize.

The term for this is "oiled doublet" and should be an easy repair.

If you are satisfied with the quality of your images, don't bother. But it could be the cause of reduced sharpness or other defects.

Thank you so much for the reply! Really interesting! I didn't know anything about fluid. I'll research further. Thanks so much for taking the time! I appreciate it.

Neil Grant · Jul 16, 2024

...I'm not sure I agree with 'zoo'. The optical section attached is for the original non-floating element 65mm lens and not the 65mm C lens in question. Also, separation normally occurs at the lens periphery and not the centre. The RB wide angles with floating elements can spill oil from the helicoid - it typically ends up on the diaphragm or the shutter rendering them sticky and slow in operation. Not sure they're particularly known for seperation.

zoo · Jul 16, 2024

Neil Grant said:
...I'm not sure I agree with 'zoo'. The optical section attached is for the original non-floating element 65mm lens and not the 65mm C lens in question. Also, separation normally occurs at the lens periphery and not the centre. The RB wide angles with floating elements can spill oil from the helicoid - it typically ends up on the diaphragm or the shutter rendering them sticky and slow in operation. Not sure they're particularly known for seperation.

That's entirely reasonable. I do not have a copy of this lens nor have I disassembled one, so I do not know for sure what the issue is. I had written off the possibility of an oil leak based on its position in the original photographs but I suppose it is possible.

Mamiya RB67 Sekor C 65mm f4.5

MichaelMcC

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Mamiya RB67 Sekor C 65mm f4.5

MichaelMcC

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MichaelMcC

Neil Grant

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