TxGR

No, I don't think this is cemented. I am grateful to @rodeo_joe1 talking me off the ledge of using a polishing compound. I read some more posts, blogs, articles, all of unknown origin. I decided to try the alcohol and windex cleaner mix solution with a lens cloth (yes, probably the scratching microfiber variety, but it came with a Hoya lens, so if Hoya is selling it...). I noticed some tentative progress. This face of the element was perfectly flat, so I put the cloth down on a flat surface and just continued working it. It seems to have done an excellent job of clearing it up. If it was a fouled/corrupted coating, I rubbed the coating off. If it was some sort of calcium or other deposit, I rubbed it off. Did I scratch the lens? Probably, but I can't see any cleaning marks. Did I introduce an irregular shape or cause there to be an undulating surface? I doubt I could have done much damage in ~15 minutes of work with a lens cloth and non-abrasive fluid on a flat surface. Here is what it looked like after I finished: Here are side by sides of before and after over the box: I put everything back together and went through a roll of Ilford HP400 and a roll of Rollei Crossbird color. I have two rolls in other cameras I want to finish, then I will send them off for processing. I'll post the results here. Of course, I have no idea what the before pictures looked like, or even if the camera has any light leaks or some other issue, so the pictures might not turn out even if the lens is good. Still, I am hopeful the results will show if I introduced any flaws of distortion. As I mentioned, I have two more showing up soon, so if one has a decent lens, I can swap it out. The viewfinder is exceptionally bright, corner to corner even in daylight, so I hope this one turns out good. Thanks for your input.

That's part of the reason I am confused: the rest of the camera is pristine, almost as if brand new. Even the other lens elements are excellent. I wonder if a previous owner tried to "clean" it with something corrosive. These cameras were made late enough, they probably have some coatings on them, so a chemical reaction with a coating would explain the even nature of the haze. Having lived aboard boats extensively, I've never seen salt water or salt spray affect glass like this. Even if allowed to dry, leaving a salt residue, cleaning the lens/glass is easy. The metal on the other hand, is easily ruined. I have two more Primo JRs I bought recently. All of them were very inexpensive. Unless their elements are similarly ruined, I will just cannibalize one to fix the other. Thank you very much for the input. I went out and bought some polishing compounds, but I'll hold off on using them until I completely give up on this element.

The inner taking lens group on a Tokyo Kogaku Primo JR TLR appears frosted or hazy: This on the lens facing the shutter, of the group between the shutter and the film plane. There appears to be corrosion around the rim of the element. It almost appears frosted, like ground glass. The haze is not opaque. There are some specks, but my concern is the haze will cause the image to be blurry/soft and blocks lights. All the other lens faces are clear. This is the opposite of the same lens group - perfectly transparent (the flecks are from the opposite hazy surface. I would expect most surfaces to be in similar condition, with the exposed surfaces being in the worst condition. On the frosted side, the roughness is very even, almost as if it is ground glass. I would have expected chemical etching or contamination to be inconsistent with rough and smooth areas. Here is the lens with some isopropanol (>90% alcohol) applied to half, drying. As it dries, the even nature of the frosted surface is shown. Based on what I've read, my best bet is some sort of windscreen polishing compound. I've read about soft erasers, alcohol (obviously did not help), vaseline (seems like a horrible idea), fine sand paper, or even baking soda. The next step, of course, is irreversible. If anybody has some other suggestions, comments, or cautions, I'd very much like to hear them before I try to polish this out. Thanks.

Well, that is good news. I appreciate the link. I can see now the brass barrel retracts and extends with the focusing ring. I looked at several other LSM Canon lenses for sale and all of them had the same barrel without the threads. The focus ring is smooth throughout the range. The glass is so clear and bright, perhaps the lens is newer than I thought. Thanks again for the responses, Brian

I came across a very nice Canon 50mm f/1.8 lens advertised as M39 Leica Screw Mount. Everything looks right except the brass collar shaft that is normally threaded is smooth -- there are no threads. I'm new to Leica's, but all the LSM/M39 lenses I've seen have an outer steel collar ~39mm in diameter and then an inner brass collar that is threaded on the outside. The measurements are correct, but the brass collar is missing the threads. I will try to add a photo. If anybody can tell me what this is, if it could work in a Leica II or IIIb, or if it could be made to work (e.g., could I replace the brass collar with a threaded collar). I am also curious about the history surrounding this unusual mount. Cheers, Brian