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Harryrag
Tinkerer
Username: Harryrag
Post Number: 75
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 10, 2009 - 11:29 am: | 
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Front lens element shows haze-like traces between inner lens elements. I guess a previous owner probably applied too much heat on knocking down the lens, at least I cannot think of any other reason for this strange thing.
What I need to know is how the lens elements are grouped together and, what is more important, how to dismantle the lens to the bone. Is regluing an option? |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 76
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 11, 2009 - 04:14 am: |
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Could not wait for an answer any longer and went straight into the lens by means of protewctive tape, hose clamps, a rubber glove and solvent.
Yep, scratches along the glue-fixed retaining nut on top of the front lens half reveal someone has tried dimantling the lens for a reason I do not know and obviously failed. The tracers one can see are caused by half melted lens glue between the two-piece group facing inward most probably caused by over-heating the lens group as a whole.
It will not be easy, but complete separation and regluing is the only way of restoring the lens, I guess. Remains of old excess glue around the blackened outside of the lens could be easily removed with acetone, so I believe canada balsam was used and will be used again to help settle the matter after carefully separating and cleaning the glass elements.
Have done that before with a Yashinon which has survived the procedure unharmed. |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 77
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 12, 2009 - 04:07 am: |
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Mission accomplished, but it was easier said than done.
After soaking the rearmost two-element lens in acetone the two glasses came apart this morning, black paint around the glass collar is still ok., but ...
... there was a broad seam of Newton's rings on the smaller glass, like that "self-coating" on old uncoated front lenses. I know by experience that it is not easy to remove this rainbow-like pattern without ruining the lens. The Yashinon mentioned in my previous post looked the same.
I think in this case that "coating" was perhaps a secondary effect of lens separation.
Can anyone confirm or correct this idea? What causes this effect?
Does anybody know whether fungus can leave such colouful traces of its presence? |
Gez
Tinkerer
Username: Gez
Post Number: 99
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 12, 2009 - 04:45 am: |
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Thanks for sharing your results with us. Are you certain that all the old adhesive has been removed? It is only a guess but the previous "repairer" could have applied canada balsam over the original methacrylate cement?
BTW, how did you manage to accurately center-up the 2 lenses? |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 78
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 12, 2009 - 06:18 am: |
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There had been only canada balsam or another glue removable with acetone between the lenses, and except what was left of the rainbow "coating" after very gently polishing the glass with toothpaste the glass was free of any residue. Polishing too much will destroy the lens, cf this thread https://kyp.hauslendale.com/classics/forum/messages/2/14889.html
Centering lenses is a problem. I had marked them with a pencil to be able to get them together again in that position. If you just leave them alone after putting glue between them they will very probably shift out of place. In that case reinstalling them where they belong is not possible as there is no play or gap in the lens container ring.
Last time I used three old bino prisms as fixing brackets around the two halves to keep them in place, but this time that method failed because of the collar of the bigger lens. So I decided to put only as much Canada balsam on the downward lens to prevent any excess from flowing out, and because I wanted a thin layer between the leses anyway. After applying the balsam and carefully pushing them together to make some air bubbles vanish I put the freshly glued lens pair back into its black cylindrical container in order to let the glue settle there which I suppose will at least take a week. Careful pushing against the downward lens shows that there is no glue on the outside of the lenses, so they can be lifted out again if necessary.
Using Canada balsam too liberally will soon result in a very sticky mess, so one has to be very carefull not to smear it all over one's workplace. |
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