medalist ii Kodak Medalist II rangefinder part question - longshot

[richard_k2]

I recently picked up a Medalist II in cosmetically good shape in hopes that it worked. The seller didn’t know how to check operation so I took a gamble. As it turns out, it works quite well. Or I should say, it worked well for a while. Somewhere into the second roll, the upper half of the rangefinder split image disappeared. 

I went home and (gently) pulled off the finder cover assembly to take a look. The problem was immediately obvious. The topmost of the pair of coincidence prisms came loose. I looked at the repair manual for clues as to how to refit it back into position, and basically find that back in the day, the coincidence prisms were ordered as a complete assembly with the erecting prism. 

So on a scale from 1 to oh crap, just how bad off am I? Is there a way to reattach that loose prism?
 

Edited July 22, 2023 by richard_k2

[hunter_compton]

You would probably need to be more specific about what parts of the prism assembly detached. Can you include a photo? 

If it's just the top prism that came loose from it's mounting, it's not difficult to re-install it, as it is just held in place by a pair of screws in it's mount. Just make sure to have the small triangular metal plate or plates present on each side, as they prevent the screw from cracking the prism when tightened. You want to tighten the screws until the prism is held, but don't over tighten, you don't want to crack it. A drop of shellac or lacquer (nail polish works fine) placed where the screws enter the frame can prevent them from coming loose again.

The most difficult part of working on the rangefinder prisms is keeping them clean while working on them as fingerprints or dust will show up in the rangefinder image. Q-tips, canned air and soft tweezers help with this. 

[richard_k2]

On 7/22/2023 at 7:42 PM, hunter_compton said:

You would probably need to be more specific about what parts of the prism assembly detached. Can you include a photo? 

If it's just the top prism that came loose from it's mounting, it's not difficult to re-install it, as it is just held in place by a pair of screws in it's mount. Just make sure to have the small triangular metal plate or plates present on each side, as they prevent the screw from cracking the prism when tightened. You want to tighten the screws until the prism is held, but don't over tighten, you don't want to crack it. A drop of shellac or lacquer (nail polish works fine) placed where the screws enter the frame can prevent them from coming loose again.

The most difficult part of working on the rangefinder prisms is keeping them clean while working on them as fingerprints or dust will show up in the rangefinder image. Q-tips, canned air and soft tweezers help with this. 

Thanks for the info. I don’t have a photo handy. The issue is with the two stacked coincidence prisms, essentially two right triangles, one atop the other. The top prism is bonded to the lower prism with some sort of optical cement. From chatting with Dan Daniel, I’m using a Loctite glass glue product, although I have a more specific optical cement on order. So far, the fix has worked, although the Loctite product is thicker than whatever magic goo Kodak used back in the day, meaning that the dividing line is thicker than it used to be. I think I could improve in my first result if I could find some way to clamp the two prisms together while the glue sets, but these are damnably tiny parts and I have not yet found a solution for keeping the prisms aligned while squeezing them together.

 

edit: I found a picture, but it’s of the bottom prism only, this was taken after the top prism fell off. 

Double edit: I circled the wrong version of the prism in the model diagram above. I should have circled part 94048  

Edited July 29, 2023 by richard_k2

[hunter_compton]

Richard, 

If the remnants of the original cement are still on the old prisms, that's going to increase the thickness of the dividing line. I'd try to remove that first before re-gluing. I believe Kodak originally would have used Canadian Balsam as cement for these prisms, try a bit of acetone to remove the old glue. If that doesn't work, Xylene will remove the old glue. Whichever solvent you use, just apply it very sparingly with a q-tip. Too much solvent will separate the bottom prism from its mount. 

I've used the glass glue Dan has recommended, and while it works, it's less than ideal. It is a cyanoacrylate glue too, so it can be prone to fogging glass, which can be a problem for optical surfaces. I think it's a smart idea to use a quality optical cement. Norland Optical Adhesive formula 61 (NOA61) is a glue that I have used for this purpose before. It's a UV curing adhesive, so the parts only need to be lined up and then a UV light shined on them for a short period of time. (the sun also works). However, I am sure any quality optical cement would work. 

 

[richard_k2]

6 hours ago, hunter_compton said:

Richard, 

If the remnants of the original cement are still on the old prisms, that's going to increase the thickness of the dividing line. I'd try to remove that first before re-gluing. I believe Kodak originally would have used Canadian Balsam as cement for these prisms, try a bit of acetone to remove the old glue. If that doesn't work, Xylene will remove the old glue. Whichever solvent you use, just apply it very sparingly with a q-tip. Too much solvent will separate the bottom prism from its mount. 

I've used the glass glue Dan has recommended, and while it works, it's less than ideal. It is a cyanoacrylate glue too, so it can be prone to fogging glass, which can be a problem for optical surfaces. I think it's a smart idea to use a quality optical cement. Norland Optical Adhesive formula 61 (NOA61) is a glue that I have used for this purpose before. It's a UV curing adhesive, so the parts only need to be lined up and then a UV light shined on them for a short period of time. (the sun also works). However, I am sure any quality optical cement would work. 

 

Thanks. I found that a small amount of acetone on a chunk of melamine foam did a good job removing the old adhesive. Pulled it all off as a single layer of goo. I tried the Loctite product (sparingly!) and got decent results. I also tried a thinned out PVA glue and got better results. I have a tube of hypo cement for optical purposes I got from Amazon, and while I like the needle dispenser, I think the stuff’s too thick still. In any case, I still have a clamping problem in that I am sure the bond layer is much thicker than it should be because I haven’t figured out how to apply pressure while whatever I use sets. 
 

This became more obvious to me as I just got a second supposedly non-working Medalist in the mail today. The split view  has a dividing line so much finer than my first Medalist that I’m now assuming the first one was already reglued at some point. 

as an aside, it was your YouTube video on how to disassemble the shutter on this camera that inspired me to pick one up in the first place. So thanks so much for that.    Given that both of these cameras were sold as non-working, I figured they’d be good learning projects.  Now that I realize that they are both cosmetically good as well as functional, I’m going to ship them off for a ‘real’ CLA rather than potentially booger them up myself.