Advice on cementing a beam splitter mirror.

[Sporriegetta]

I've recently landed a DeMaria Lapierre Telka III in pretty decent condition. Unfortunately the beam splitter was pretty grubby. I found a company that can clean and recoat the mirror for me for only a few quid so I decided I'd take it out and send it off. Thankfully the mirror wasn't that bad but it had a coating of film - possibly the old glue, that was causing the blurriness. Because it was going off to be recoated I figured I'd have a quick go at cleaning it myself - and it's come up pretty jolly nice. I sat it in place carefully, looked through the viewfinder and it looks great. The next trick is cementing it in in a position that is close enough to use the camera's adjustment screws to align the rangefinder view correctly. I'm thinking that if there's a cement that can offer some resistance - kind of syrup like I guess, I could fine tune the positioning by eye then do the final adjustments. A cement that isn't going to gas off and create new problems down the track would be ideal. So my question is, is there such a product? If not what is the best product to use?


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[mooge]

Like an optical cement or a regular glue?

I use canada balsam for gluing optical bits together. two part epoxy has worked well for me to glue things near lenses at least. I think it's cyanoacrylate (super glue) that gases off and leaves some haziness.

Where did you get the mirror recoated? I might want to redo my M2 viewfinder (again)...

 

[Sporriegetta]

Like an optical cement or a regular glue?

I use canada balsam for gluing optical bits together. two part epoxy has worked well for me to glue things near lenses at least. I think it's cyanoacrylate (super glue) that gases off and leaves some haziness.

Where did you get the mirror recoated? I might want to redo my M2 viewfinder (again)...

It's the morning after the night before! Everything changed. I found I was able to clean my mirror and not ruin the coating so I've now done that. You can get it done though at scientific mirrors in London for between £10 and £20 though. http://www.scientificmirrors.co.uk/vcsm-Aluminising.html spoke to them on Monday and those prices are current.

So I used 2 part epoxy in the end. Prior to that I tried heat glue but it didn't bond well. So far so good although I'm yet to take it out. I'm going to run a roll of film through this morning. As for out gassing I can't find any specific info but other 2-part epoxies gas a lot when curing but very little after that. Fingers crossed!


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[Sporriegetta]

Still sitting nicely. No major knocks to test it but. Little to no expansion or shrinkage during curing it would seem.


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[mcfingon]

It still may move a little over time, like several months, from my experience with a professionally-replaced mirror in my Leica III. But it is just a matter of checking periodically and re-adjusting the rangefinder setting to compensate.

 

[Sporriegetta]

Ah ok. I can adjust horizontally with ease but vertically I'd need to break the mirror off and re-glue. I'm kind of prepared for that and am considering modifying the plate so as to be able to make it adjustable. I suspect with there being 2 brass rivets under the mirror plate and one third nodule on the camera top for the plate to locate onto, you simply filed them to align the mirror. Obviously I could be wrong though and it could be a simple turn of a screw!


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