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Wayne
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, November 30, 2005 - 04:02 pm: | 
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I have a cemented lens element that has seperation causing what appears to be concentric rings of the glue or cement between the elements. I seem to recall reading somwhere that someone fixed a similar problem by heating the elements in a 200 degree oven. Supposedly this allows the balsam cement to melt and reseal. Has anyone heard of this or tried it? And do I have anything to lose trying it? It is from a Vivitar zoom lens.
Wayne |
wayne
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, November 30, 2005 - 05:48 pm: |
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Hi Wayne (from another Wayne)
I'm not sure when balsam was superceded by more modern optical cement, but I doubt it was used in your Vivitar lens. I don't know if the heating trick works with the modern synthetic cements, but it did more or less fix a separation problem in an old Rollei doublet I had. I didn't do the heating - somebody else was trying to separate the elements for me but the heating process melted and redistributed the cement, effectively curing the problem. I've used methylene chloride to separate elements glued with synthetic cement, without resorting to heat. Of course you then have to clean up the elements and recement them. Summers Optical sell a wide range of optical cements, and I've found the UV curing ones very easy to use (I think I've got type J-91).
Cheers
Wayne |
rick
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, November 30, 2005 - 09:13 pm: |
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Separation generally does not have very serious consequences in terms of performance, though it's a big deal cosmetically. Depending on where this element/group is in the zoom lens, if you can't live with the separation you may find that it would be a whole lot less trouble and not much more cost to replace the lens. |
Wayne
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, December 01, 2005 - 05:11 am: |
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Thanks Wayne for the reply. I suspect you're right in that my lens is more likely to have a synthetic cement. I hadn't thought of that. Who knows how it would react to heat?
And Rick, I think I'll take a hint from your suggestion and try reassembling the lens and give it a test to see just how it does perform. The element group is an inner element in a Vivitar Series 1 28-90mm.
Wayne |
wayne
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, December 06, 2005 - 07:18 pm: |
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Just as a follow-up, I reassembled the Vivitar 28-90 Series 1 lens and went out and tested it against some other similar zoom lenses I have, using Kodak E100G slide film and a tripod. It certainly wasn't a scientific test, and wasn't shot on a map or test chart, but using an 8x loupe and light table, I could see no difference in the slides that came from the lens with seperation.
Thanks Rick and Wayne for the advice.
Wayne |
John Shriver
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 10, 2005 - 12:27 pm: |
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I've done baking of a balsam cemented lens group (a Leica Summar), because the group is peened into the lens mount, and the lens was in such ghastly condition that it wasn't worth caring about.
The balsam did melt, and with some pressure I greatly reduced the amount of separation. I did cause a lot of little bubbles. It went from having ghost images to just being fuzzy.
I managed to upgrade a wretched lens to a bad lens. Doesn't do anything about the brass filings trapped between two elements, where one was put back with epoxy. (The efforts of the butcher who ruined this lens.)
John Shriver
http://john.shriver.home.comcast.net |
