optical cement?

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mooge

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Hey guys,

I dropped my M2 again (ugh...) and now the beamsplitter has split. And CRR Luton isn't taking repairs in until June. and I kind of like this camera alot and I don't want to wait that long.

Any suggestions on where to get optical cement? and how permanent is it-- if I mess up the alignment is the finder doomed forever?



Or should I just bury the remains in my backyard and buy a Bessa?

advice, condolences, etc appreciated...
 
It is a straigt-forward fix. Note that I didn't say easy, but, straight-forward.
Youxin Ye will also do it for you, check his web site at http://www.yyecamera.com/

Anyway, if you want to do it yourself, get some optical cement here, and research how to cure it: http://www.optical-cement.com/cements/products.html#anchor720308

I use Type UV-69, http://www.optical-cement.com/cements/cements/uv.html#uv69

You have to take the rangefinder off, and push out the prisms.

And you have to make a holding fixture to hold the prisms together while you cure it.
It isn't as hard as you think. There is paint at where the prisms are attached, and if you are careful, you can use the paint outline to position the prism. But you must hold the prism in place, as when you add the adhesive, the prisms will slide against each other. And you cure it with a sun lamp, or a UV lamp that you can buy at a hardware store.

I've done it three or four times.

And I"ve cured it for a couple days, to make sure that it does cure properly. In the curing chamber (a large soup pot for me), put a dab of glue next the the jig, and when the dab of glue is hard, then I used that as my 50% point.

Good luck
 
If you are worried about permanency you might want to consider using Canada Balsam instead. But you really need to know what you're doing with that too, it may need to be diluted with a little xylene. And I don't know enough about Leicas to offer an educated comment about the impact any slight changes in the refractive index between the balsam and cement would have on the brightness of the finder and focus spot, etc. It's something I would not jump into without some careful research frankly.
Regards
Brett
 
Yes, with the UV cured glue, you won't ever get the prisms apart again.

With Balsam, you can dissolve the glue bond, with a week or so of soaking in methylene chloride (ie. paint stripper).

I've done that too ;-)
 
UV glues can be separated with paint stripper. Takes 3-5 days.
I use "Parks" brand. Don't know if some of the environmentally friendly varieties work.
rubber gloves & safety goggles are recommended.
Burns like a son of a gun if it's not washed off immediately. Learned that the hard way.
 
Milsolve will apparently separate optical cement too, but I have been told that days or weeks of soaking may be needed to effect separation, it is tenacious stuff by all accounts.
Regards
Brett
 
thanks for the replies guys! lots to think about...

Vick--
how do I push out the prisms? I thought the beamsplitter was held in on a sort of pivot thing...
(and Austenite bay is a place on an iron-carbon phase diagram... I'm actually in Ottawa)


thanks everyone!
 
Mooge

Have you taken the RF off yet?

There are a couple metal pieces that hold the prism on, but ultimately you have to push it right out.

You will need to fashion a tool to push without damaging the prism.

Let me know if you want to give it a go.

I'm in Ottawa too
 
Vickko said:
And I"ve cured it for a couple days, to make sure that it does cure properly. In the curing chamber (a large soup pot for me), put a dab of glue next the the jig, and when the dab of glue is hard, then I used that as my 50% point.
Click to expand...

It might be a good idea to place some sheet glass or some lens element from the box of spares (suspended on spacers so that it does not touch) above that test dab - that way you don't risk underestimating the UV absorbing characteristics of glass.
 
I haven't taken the RF out yet but I did take the top plate off to take a look around. There's a loose prism for sure...

so I guess I'll buy some Canada balsam then. And apparently I can use it to treat my cold too!

maybe this would work okay?




edit: do I need to worry about what the balsam is dissolved in? does it have to be xylene?
 
mooge said:
I haven't taken the RF out yet but I did take the top plate off to take a look around. There's a loose prism for sure...

so I guess I'll buy some Canada balsam then. And apparently I can use it to treat my cold too!

maybe this would work okay?

edit: do I need to worry about what the balsam is dissolved in? does it have to be xylene?
Click to expand...
I should think so, xylene is the substance that has always been referenced for diluting it in all my research on repair techniques. I have no idea if alternatives would also work, but if xylene will not adversely affect the stability of the balsam, and promotes the best possible refractive index of the assembled unit, I don't know why you would try to use anything else, particularly with a valuable camera such as a Leica. There are one or two chemists in the forum membership. Perhaps someone can offer a more enlightened opinion.
Regards,
Brett
 
Wikipedia says that Canada Balsam is either dissolved in Xylene or "essential oils" (plant oil). Neither seems severely toxic. I'd be more interested in which one evaporates best, to leave the balsam adhesive behind, properly bonding the prism.

I think you can do the repair without having to remove the rangefinder optical assembly from the body. It would save some time, in not having to take it all out, including the RF sensor arm.

You do need to get the two prism halves out, and if you have already taken the top off, the prisms are easy to get to.

I think you remove the cover plate at the rear of the rangefinder, and remove the prism from the rear (push it out from the front).
 
Yeah, from what I understand from the wikipedia article, balsam either dissolved in essential oil or xylene was used as optical cement, so if that's correct, I guess either would do... but on the other hand, everything I've read on canada balsam as an optical cement has mentioned xylene as the solvent. hmm.

If I recall, there were a couple set screws for the rear prism, so I don't know if I can leave the RF where it is. actually I probably have to take it out anyways because the framelines are sticky.

But then, once I get the stuff out, what should I clean the prism surfaces with? I don't want to lose the semi-silvering (that would be bad)... and do I have to worry about the silvering being oxidized in the meanwhile? I'm not going to start working on this for another week or so.



thanks again, guys!
 
Carefully clean the prism surfaces with acetone.

Two good posts are here, for DIY

http://forum.mflenses.com/viewtopic,p,1089900.html

http://www.cloudynights.com/ubbthre...889/page/40/view/collapsed/sb/5/o/all/fpart/1

I don't know how long it takes to oxidize the silver. The cameras that I fixed had fully separated prisms, and I don't know how long they had been that way. But after they were re-cemented, I couldn't tell them apart from rangefinders that were never repaired.

But I do suggest you be gentle with the cleaning. You certainly don't want to abrade off the silver coating. Just clean enough to clean off any remaining adhesive.



mooge said:
...But then, once I get the stuff out, what should I clean the prism surfaces with? I don't want to lose the semi-silvering (that would be bad)... and do I have to worry about the silvering being oxidized in the meanwhile? I'm not going to start working on this for another week or so.



thanks again, guys!
Click to expand...
 
I use acetone on a Q-tip to clean my lenses too-twice each time followed by a clean/ dry Q-tip. THEN I use a weak solution of a few drops of liquid dish washing soap/ 1 qt. of distilled water on a Q-tip twice to clean off the acetone residue, each time followed by a clean/ dry Q-tip also.

I would follow the same procedure on the prism surfaces.






Vickko said:
Carefully clean with acetone.

Two good posts are here, for DIY

http://forum.mflenses.com/viewtopic,p,1089900.html

http://www.cloudynights.com/ubbthre...889/page/40/view/collapsed/sb/5/o/all/fpart/1

I don't know how long it takes to oxidize the silver. The cameras that I fixed had fully separated prisms, and I don't know how long they had been that way. But after they were re-cemented, I couldn't tell them apart from rangefinders that were never repaired.

But I do suggest you be gentle with the cleaning. You certainly don't want to abrade off the silver coating. Just clean enough to clean off any remaining adhesive.
Click to expand...
 
so I got the Canada balsam in the mail (from fleabay) and I've just set up a few test specimens to gauge curing times, strength, etcetera. a few observations:

1. it's a yellow viscous fluid. I was worried it would be runny.
2. it's sticky and won't come off your hands with water. Like sap. which is actually not that bad since...
3. IT SMELLS REALLY GOOD!
 
heat? aww nuts... any suggestions for temperature and time?

and how will this probably destroy the silvering?

I'd send it out if CRR Luton was taking repairs now and I had a spare three hundred bucks, but they aren't and I don't...
 
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