View Full Version : Fixing Balsam Separation

19-Feb-2017, 14:07
I have a small rapid rectilinear lens on my Prosch shutter, and noticed the front element (only) has begun to get crazing/separation. The glass appears to be pressed into the brass insert. I wonder if the lens was in my hot car last summer and that caused this? Can anything be done?

Kent in SD

Richard Wasserman
19-Feb-2017, 14:21
I would talk with John Van Stelton— http://www.focalpointlens.com/

He recently repaired a Rollei 3.5 F lens for me that had developed severe separation and it now looks, and works, as new

Steven Tribe
19-Feb-2017, 14:53
Looks like separation, rather than devitrification, due to the line/phase areas.

Rapid Rectilinears were made in the mass production era, so usually glass is mounted by lathe turning over a thin brass edge over the outer mm or so of the glass.
Can be "opened" manually with a hobby knife, working the edge back slowly with many turns. Protect lens surface and your fingers. expect some damage to the raised brass rim. I always mount the lens again in black mastic to make sure not to rely on the damaged rim edge.

21-Feb-2017, 06:33
Kent, here is what I did a few years ago - had a RR with bad balsam separation - removed the affected cell and let it soak in a container of acetone - took at least a week before I could see that it was beginning to work (the balsam started to dissolve and leak out from between the cell) - after about two weeks I could gently work one lens element away from the other and before long they were separate. Cleaned them up with fresh acetone then dried, washed in warm soapy water, rinsed and dried.

I did not want to go thru the process of re-cementing them together so I put a drop of cooking oil (Canola oil) in place of balsam or glue, worked out any air bubbles, put the lens back together and used it that way for about a year until I sold it (disclosing to the buyer my modification). Anyway, after a year, the cell with the Canola oil looked perfectly clear and the lens performed fine. If after a few years it might begin to cloud over, it would be a very easy fix.

Kevin Crisp
21-Feb-2017, 09:06
My impression is that RR lenses are much more sensitive to heat in the separation process than many other lenses. Almost like the glass is more brittle. (Steve Grimes was doing one of mine with his heat technique and it shattered.) I would dissolve what is there in acetone or MEK. Be patient, it can take a week or more.

21-Feb-2017, 09:37
The oil idea is interesting. I did some reading a while ago and was surprised that telescope makers do this with the huge objectives they make, expecting, I guess, that they will last forever.