Quarter Moon Shadow in Mamiya-Sekor c 1:4.5 f180mm lens

[paul ron]

Last year I bought a Mamiya 180/4.5 - some dust in the optics - and just now I see a very minor darkening similar to what was shown above. It's at the very edge of the element(s) and I don't think it would have an effect even wide open.

Is the area likely to expand? If so, how rapidly?

Also just realized the shutter is behind the rear element - it could be touched.

Just keep your fingers out of the hole.


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[shutterfinger]

About recementing lens. Several years ago I purchased a 12" Goertz Dagor in Compound shutter from Keeble & Shuchat, Palo Alto, that was cloudy.
I decided to recement the offending cell so I disassembled the lens. I put the cloudy cell in a 250°F oven for 30 minutes but the elements would not budge. Next I put it in a container of boiling water for several minutes but it still would not separate. I did not want to crack a cell so I did not place it in direct heat (gas flame) and did not go above 300°F with the oven. The oven was heated to temperature, turned off, then the cell placed in the center of the oven. After several cycles I gave up and reassembled the lens, wrapped it up in protective cloth, and put it aside for a rainy day. Six months later I took the lens out to try again and the cloudy cell had cleared. Apparently the heat then cool to room temperature procedure caused the balsam to heal itself during the rest. I sold the lens a few months later and it was still crystal clear.

You may only need to warm up your Mamiya cells to get the cement to seal itself again.

 

[Dan Fromm]

Hmm. Modern lens, modern cement is much more likely than Canada balsam.

 

[Theo Sulphate]

How rapidly or slowly does this separation occur (I realize environmental or other factors might influence this)?

The shadow on my lens is maybe 3mm at most - a thin crescent. I hope it'll be much longer than 7 days before it becomes waxing gibbous.

 

[Kirks518]

This thread got me thinking; could lens element separation be accelerated by a warm/hot climate? Ie, too frequent time spent inside of a hot car, etc?

Theo, I have a couple of lenses that have minor edge separation, and it hasn't progressed in the years I've owned them, if that helps any. Of course, YMMV.

 

[shutterfinger]

One needs to know what type of adhesive was used on the Mamiya lens cells and the manufacturer of the adhesive to find how to remove it.
Heat is a key component in breaking the UV adhesive bond. Norland recommends 400°F to 800°F and using a hot plate as described in SKGrimes article linked to in post #23. Norland also states soaking in liquid paint remover for several hours to a day or two will work, the length of time will depend on how large and thick the lens.

The separation may be caused by the bonding technique or type of adhesive used. If you have a black car with untinted windows and parked it in direct sun with the lens laying on the seat or dash for a few 100°F+ days then maybe the interior temperature of the car may have caused the failure.

 

[tedr1]

Here is the example of a NIB Mamiya 180 showing element separation, this is a Sekor C for the RB67 so the age could be as little as ten years or as much as thirty years, very unlikely to have been outside the warehouse, it probably sat on a shelf it's whole life.