| Author |
Message |
    
Harryrag
Tinkerer
Username: Harryrag
Post Number: 17
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 14, 2008 - 03:40 am: | 
|
How can lens elements be separated if they are not glued together with Canada balsam but with more modern glue? |
Mikel
Tinkerer
Username: Mikel
Post Number: 113
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 14, 2008 - 06:26 pm: |
|
If it is a modern epoxy you are just SOL.
That would mean that you are out of luck. I've tried heat and everything I could think of to to solve it but without success. |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 18
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 15, 2008 - 03:06 am: |
|
The problem I have to solve is getting the two element front lens group of a no-name 75mm enlarger lens apart so that the old glue (epoxy?) between the lenses can be replaced, as it has gone opaque. You are right Mikel, I also found applying heat to be useless.
I have soaked the lens group for about two weeks in acetone which has very slowly but considerably reduced the fogginess of the glue, starting from the edge. But this seems only a temporary solution.
I was told that silicone remover, given enough time, may soften any sort of glue. Any ideas on that? |
Sevo
Tinkerer
Username: Sevo
Post Number: 5
Registered: 09-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 15, 2008 - 07:06 am: |
|
Modern glues most often are acrylates. Sometimes, a few weeks in a jar full of acetone will work, but more often, you'll only manage to separate the edges, making matters worse.
That is, nothing short of the separating solvents sold by the glue manufacturer is guaranteed to get them apart without damage - but even for that, you'd first of all have to figure out what glue is in there, and besides, many of these solvents are way too toxic for casual use, and won't even be sold to anybody who does not have a certified lab.
Silicone remover will most likely do nothing at all unless the lens is glued with silicone (very unlikely). Chloroform and the like would do the job, but probably at the price of quite a bit of health damage - you'd have to find a company which has the equipment to handle that stuff safely... |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 700
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 15, 2008 - 03:14 pm: |
|
I'm surprised that a no-name 75mm enlarger lens would even have a cemented group, the ones I've seen have been triplets. |
Norman
Tinkerer
Username: Norman
Post Number: 3
Registered: 03-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 15, 2008 - 05:09 pm: |
|
What a coincidence! I logged on to look for advice on regluing already separated elements. Can anyone help please? |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 19
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 16, 2008 - 04:10 am: |
|
Norman, you can use the "search" button; under the keyword "Canada Balsam" there is lots of info on that, H.
Rick, this one has a "no-name"-name, it is a "Kestrel" 4,5/75mm, a very solidly made E.L. which I have kept stored away in my darkroom for at least two decades without touching it. I have never used it for darkroom purposes but as a bellows macro lens. What would there be inside, i.e. between what think is a front glasses if it was only a triplet? |
Norman
Tinkerer
Username: Norman
Post Number: 4
Registered: 03-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 16, 2008 - 04:09 pm: |
|
Thanks Harry, of course I know of canada balsam but I was hoping that someone could tell me of an easily available glue to use. Maybe I did not explain myself, but I do not want to buy a large quantity of adhesive to fix one 13mm pair of lenses. Is it possible to use super glue? |
Nickon51
Tinkerer
Username: Nickon51
Post Number: 33
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 17, 2008 - 01:07 am: |
|
G'Day all
Norman, Surplus Shed here http://www.surplusshed.com/pages/item/b1077.html
have some Canadian Balsam, sold in relatively small quantities.
Super Glue doesn't stick to glass. It appears as if it will but it falls apart after a few days. It also won't give you any time to set the lens correctly before it sets.
The modern glue is a UV cured epoxy with the correct optical refraction. Epoxy gives you enough time to optically set the elements before setting.
If its a good lens it might be would be worth sending out to get properly done, if its not then I doubt than any cementing that you can do at home would be worthwhile.
If you hold then lens under a lamp, you can count the number of reflections of the lamp that you can see in the lens. Every glass air surface will give you a reflection. You will have to move the lens around a bit to see.
Good luck with your project.
Cheers
Greg |
Harryrag
Tinkerer
Username: Harryrag
Post Number: 20
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 17, 2008 - 01:30 am: |
|
Somewhere in this forum I read peolple used clear acrylic car paint, the sort that is used last as a protective layer on metallic lacquer. In my understanding super glue is perhaps a way of no return, it probably cures too fast, and its optical qualities are at least uncertain.
I am still stubbornly searching for a solution to my initial problem - and found this: http://www.atmsite.org/contrib/Sapp/LensGlue/
maybe it is also useful for your purposes, if you make use of the article's last remarks in a different manner, that is acrylic "glass" plus solvent as a sort of glue. |
Gez
Tinkerer
Username: Gez
Post Number: 40
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 17, 2008 - 01:56 pm: |
|
I have had some success in separating an eyepiece doublet off a Konica. Modern lenses are sometimes glued with a methacrylate compound and this can be dissolved with dichloromethane, aka, methylene chloride. Just leave the glass to soak for 3 to 4 days, and carefully slide the pieces apart.
When it comes to re-gluing, Norland Optical cement is the stuff to use, but in the case of the non-critical eyepiece I used a glass-to-glass cement obtained from a local DIY store. It cures under UV light so it is probably similar to the Norland item. |
Norman
Tinkerer
Username: Norman
Post Number: 5
Registered: 03-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 17, 2008 - 02:01 pm: |
|
My requirement is not critical, I need to refix the eyepiece lens on a Nikon pentaprism. I live on the Falkland Islands and anything other than basic adhesives have to come by post. Also there are restrictions on many chemicals. What would happen if I used a drop of polyurethane varnish? I am prepared to accept less than perfection. I just want something that will work without destroying a perfectly good pair of lenses. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 703
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 17, 2008 - 07:06 pm: |
|
I can't imagine.... something on the surface, but if you already have the element out you've seen that it's internal, so it would seem it has to be a cemented pair. You should be able to see the seam around the edge too. Even in a Tessar type, which would be fairly fancy for a non-name lens, the front element would still be a single glass... the only cemented pair in a Tessar is in the rear. I guess you just have something a bit different, perhaps a reversed Tessar design. |
Sevo
Tinkerer
Username: Sevo
Post Number: 7
Registered: 09-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 18, 2008 - 06:06 am: |
|
Polyurethanes are strongly yellowing, and won't ever harden unless they are 2k.
If you can't get hold of Canada Balsam (the local hospital should have some for microscopy, of the liquid kind - but that could be left to dry to get some solid resin), UV hardening methacrylate (a.k.a. glass superglue) as sold for mounting car rear mirrors would do in a pinch for uncritical applications, like a finder. But I would not use it on a lens (where the wrong refraction index could cause problems), or on rare and expensive items (where the uncertain removal would seem inacceptable). |
Arnoldharris
Tinkerer
Username: Arnoldharris
Post Number: 39
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, November 16, 2008 - 04:59 pm: |
|
I recall some discussions on various camera repair forums -- possibly this one included -- about treating edge separation in a novel but effective way.
Instead of attempting to unglue that which cannot be unglued or to reglue that which is difficult to reglue outside a real camera lens factory, why not just set up the stripped-out lens unit so that it wicks up some of the right kind of the thinnest, purest most colorless lubricants into the edges of the joint, so as to fill the usually small voids?
After all, it's a useful lens unit that you really want, not just a lens joint that you and only you know for a fact solely comprises Canada balsam or impossible-to-work-with modern glue.
In any case, for most collectors, they may be no option, other than tossing the lens or using it as an elegant but pathetic paperweight.
Arnold Harris
Mount Horeb WI |
Sevo
Tinkerer
Username: Sevo
Post Number: 17
Registered: 09-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 17, 2008 - 03:09 am: |
|
From a practical perspective, people worry too much - or rather, the desire get hold of "mint" items (often by people that actually do not use their collectibles) is overrated in relation to useability.
Most lenses (and old lenses even the more so) are not anywhere near decent performance unless stopped down at least two stops, by which time the outer 3/4 of the lens surface are covered by the aperture.
A fair proportion of lenses with "repaired" edge seperation actually has a worse performance at working apertures than before the fix. The risks of re-cementing should not be underrated - centering and collimation to original factory specs either needs tools and data which are not available any more (and cannot be reconstructed economically for a single lens), a huge amount of time, or a big strike of luck.
In a nutshell: Edge only separation often should not be treated at all, as it is less likely to affect the practical lens performance than attempts at a repair. |
