Lens cell/mount adhesive

StepheKoontz · Mar 29, 2019

Today I was "refurbishing" an old Ikonta B folder. The front lens cell (front cell focusing opton tessar) is crimp mounted and while cleaning some nasty coating oxidation off the front surface, the cell popped out of the mount. I was able to pop it back in after getting it clean, but now it's not super secure and it would be easy to pop it out cleaning the front surface in the future. Is there some kind of epoxy etc that would be good for making it secure in the mount again? I was thinking some JB weld but wasn't sure if there was like "optical glue" made for something like this. I just would feel better if it wasn't this easy to pop it out of the mount for a user camera.

Stephe

shutterfinger · Mar 29, 2019

If the mount is tight enough then clear nail polish should hold it as nail polish holds as well as the thread locker used on screw in cells and camera screws used by manufacturers.
JB Weld will work but will have to be cut out if the cell needs to be removed from the mount again.

StepheKoontz · Mar 29, 2019

Clear nail polish sounds like a great idea!! It "pops in" tight enough to use it, I'm just afraid in the future, it would be fairly easy to accidentally push it in cleaning the front element. I have some UV setting clear top coat that should work well for this.

Nodda Duma · Mar 29, 2019

Don’t use clear nail polish! It outgasses so much that over (a relatively short period of) time a haze will form on the inner surface of the lens...then the camera will be useless.

Buy a tube of DOW 3145 RTV off ebay. Clean all the surfaces. If the lens has a seat you can bond it to, put a very thin layer on the seat with a toothpick and set the lens down onto the rtv. Give the lens a spin to distribute the RTV between the seat and the lens, then let it dry for several days.

If the lens has no respectable seat (like not very wide), then put the RTV around the periphery of the barrel, then slide the lens in. Give the lens a spin to distribute the RTV and let it dry over a few days.

You could also repair the crimp (tap or bend the brass in. Brass is a soft metal)

shutterfinger · Mar 29, 2019

Nodda Duma said:
Don’t use clear nail polish! It outgasses so much that over (a relatively short period of) time a haze will form on the inner surface of the lens...then the camera will be useless.

Apparently I haven't used enough nail polish per application over the last year or two or it hasn't been long enough for it to fog a lens cell. 3 places (12-2-8lcok face equivalent) about the width of the brush and relatively thin should be adequate to hold the cell.

Nodda Duma · Mar 29, 2019

In the end, it is your lens to do with as you wish... it's no skin off my back.

I'll be the first one to suggest cheap ways to repair optics if I know they'll work. However, for the benefit of someone who may search the archives in 10 years looking to repair a lens of value.... I won't recommend using adhesives with significant out-gassing, nor offer any other advice that increases the risk of ruining optics.

shutterfinger · Mar 29, 2019

I have used it sparingly on the barrel threads. I'll look for something else when and if I start repairing again.

Nodda Duma · Mar 30, 2019

Try a tube of the Dow 3145 I mention above. It is easy to work with (although as an RTV it could get out of control so use toothpicks to work with it), will do what you want to do, and isn’t entirely permanent like a hard epoxy or UV cement would be.

StepheKoontz · Mar 30, 2019

Actually it's too late. I had some UV activated clear nail polish on hand and it sounded like a good solution for this case. The "lip" that holds this small lens in place is tiny and I feared trying to do anything with it mechanically, I would likely destroy the lens. I could see RTV working well on a larger lens, especially something that there was zero mechanical retention. I wanted something I could apply after it was in place to reinforce the "almost enough" retention that is there and wouldn't RTV outgass for a while too? Given the possible outgassing from this polish and that I don't need to use this anytime soon, I'll let it further cure on the shelf for 4-6 weeks before I reassemble it. Thanks again for the ideas!

Nodda Duma · Mar 30, 2019

Not all RTV’s are the same. Dow 3145 is a low-outgassing RTV (probably better to say silicone adhesive, but we all know how RTV acts) specifically designed for these types of applications. There are newer, better variants that are priced well outside the reach of mere consumers like us, but we use this at work on prototypes and low-cost production lens assemblies when the application of an RTV-like adhesive makes sense.

For epoxy, 3M 2216 and 3M 1838 are used a lot and are probably a better fit for this application, but those epoxies cost ~$500 a tube.

choiliefan · Mar 30, 2019

I remember something from some time ago that certain silicone adhesives, when used in automotive engines, were found to out-gas and ruin oxygen sensors. Out-gassing can be a problem -- ask my wife...

John Koehrer · Mar 30, 2019

I agree with shutterfinger regarding the use of clear nail polish. I like it for the purpose of a cement to install the lens in your situation.
Obviously not for when high strength is needed.

Lens cell/mount adhesive

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