Disassembling the rear lens group on Mamiya Sekor 65mm f/3.5 TLR lens

BHuij

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My father picked up a C3 in great condition at an estate sale recently. It came with just one lens (well... two, since it's a TLR), the 65mm f/3.5. Shutter and aperture are all working great, but there's fungus/gunk in both the taking and viewing lenses.

I did all the normal "field stripping" you can do without tools - unscrewing elements from each other, etc. The fungus is definitely in the rear lens group, which easily unscrews. Unfortunately, the fungus seems to be on the inside surfaces that I can't reach. It is not on the accessible front or rear surfaces. Everything else on the lens is clean and clear.



Is there a way to access the surfaces that need cleaned, or am I SOL here? This lens is essentially useless to me if I can't get it clean, so I'm willing to try some riskier stuff if it means a chance at restoring the lens to usable condition.
 

MattKing

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Thread moved to the Camera repair sub-forum. Hope you find the information you need.
 

reddesert

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I'm not sure that's fungus, which IME has a more spider-webby appearance. Regardless, it's haze of some kind. Unfortunately, I have a 65/3.5 with haze on the inner surfaces of the rear group (viewing lens only, fortunately), and I didn't see an obvious way of opening up the rear group. It might be glued together, or worse, crimped. Maybe user Mamiya_Repair knows how it is put together.
 

reddesert

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Dan Daniel said:
Looks like a joint at the red arrows?
Click to expand...

On my lens (older, silver shutter, I don't know if they are all the same), yes that unscrews the rearmost group - probably a doublet - from the rear lens cell. But my problem is inside this rearmost group. Depending on where the OP's problem surface is, this may or may not help.
 

MattKing

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The silver shutter lenses are put together mechanically in quite different ways from the black lensess - even if they are one of the focal lengths that have the same optical design.
 
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BHuij

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Looking closely at the spot where the red arrow points, it looks like it’s either no seam at all, just solid metal, or it’s a seam that has been cemented somehow. Can’t tell for sure. What I can tell is that no amount of force I’ve been able to apply with my spanner and rubber grip around the opposite barrel is getting it to budge in the slightest.
 

ic-racer

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Some (many?) locking rings are sealed. I dribble acetone I'm the space to promote loosening the ring.
 

Dan Daniel

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Any very small set screw in the outside barrel? Maybe the split is at the side, where the threads that go into the shutter meet the solid side part. And often, but not always, there will be a set screw to hold the outer barrel in place.
 

reddesert

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This is what the rear cell of my 65/3.5 silver viewing lens looks like when disassembled. There’s no set screw, the rearmost group (on the left) just unscrews. However, the haze, which you can’t easily see here, is inside that group.
 
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BHuij

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Okay - mine appears to be the black variant of the lens, but my rear assembly matches yours, including the lack of a set screw, and the notches for a spanner on the rearmost cell. My haze appears to be in between the two cells that you've successfully disassembled here, but I guess I won't know for sure until I manage to get them apart. Here's hoping that's possible with some elbow grease
 

Kino

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Have you tried a few drops of alcohol in any joins to see if that helps loosen the grip. What's it going to do? Cloud the lens?



I have the same lens with a few tendrils of fungus in the elements just forward of the rear group, but on the back side of the shutter. Haven't yet tried to take it apart, but my rear group does have spanner notches, so the rear element came out with some mild force. Looks like I need to dismount the lens from the lens board to get to my fungus.


Good luck!
 
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