Fixing front element glass wobbling in its housing

[mrmekon]

I have a Voigtländer Color-Skopar 80mm lens with a loose front element (group?), and I'm wondering what the best way is to keep it in place. The glass is held into its housing with a crimped retaining ring on the inside, but not particularly well. The glass wobbles back and forth fairly significantly.

There is a gap between the retaining ring and the glass, so I'm wondering if I can just slip a few microdrops of something into that gap to hold it steady. Would contact cement work for this? I'm assuming that, as long as I can get it underneath the ring, it wouldn't affect image quality.

Thanks!

 

[xkaes]

A picture sure would help. I'm not sure what "a crimped retaining ring on the inside" means -- or how you can see it.

What holding it in place from the outside -- or is it merely pressed against the front with "crimped retaining ring on the inside"?

Is the front, outside barrel of the lens loose -- or just the glass?

Is there a retaining ring on the front? Can't tell without a picture.

 

[mrmekon]

Sure! The attached photos aren't great, but better than nothing.

The front lens assembly is completely removed. There's not much "barrel" to speak of, just a dead simple piece of glass held between two pieces of metal. The entire front of the housing is a single, solid piece of metal. The identifying markings ("COLOR-SKOPAR") are just on a plastic ring that isn't attached at all; it is not a front retaining ring.

If you look at the photo of the the back/inside, the black surface closest to the glass is a metal ring holding the glass in. I think it is a separate retaining ring, but it might actually be a single piece of metal with the back crimped inwards. It seems like the glass was dropped into the housing, and then either a small black ring was crimped onto the back to hold it in place, or the edges of the housing were crimped over. The glass is supposed to be wedged tightly between the front of the housing and the ring, in any case... and it is held in, but not tightly.

Only the glass moves; I can push it back and forth between the front of the housing and the rear ring. It rattles. The "retaining ring" itself does not move, and I'm afraid to try "re-crimping" it. There is enough space between the ring and the glass that I can fit the tip of a toothpick under it.

I'm thinking literally anything that sticks to glass should be fine, with three or four drops placed around the edge, under the crimped rim. Maybe even clear nail polish?

 

[xkaes]

Looks like you got it right. As long as the glass is pressed up against the front of the housing, you should be OK. You just need a glue that is not too FLUID -- because it might leak out onto the glass. Something like GORILLA GLUE might be the ticket. In any case, you shouldn't need much glue. Rubber cement/Contact cement sounds good as well. Plio-bond might be too fluid.

 

[Steve906]

I literally just did the same job with a large taylor hobson anastigmat last week. I used UV cure resin, fairly thin is actually quite good. I placed a (small) weight in the center of the glass to keep it pressed against the front and added a few drops of the resin around the back edge letting it run into the gap. As the resin doesn't cure untill you want it to it's easy to clean any excess if necessary. Apply UV light or sunlight until set. I then built up a little more around the inside rim to fill the gap, curing as required as this was a fairly heavy piece of glass.

 

[Helge]

I’d use carefully syringed daps of silicone glue. Totally reversible, should the need arise at any time in the future, and also allows a certain amount of thermal expansion and air exchange.
A tiny bit going into the image forming area isn’t going to make any measurable difference.

 

[mrmekon]

Thanks, everyone! UV resin sounds the most professional, but perhaps overkill for this 1g little old lens. And it might take weeks to collect enough sunlight in autumnal Sweden...

I tried clear nail polish (lacquer) because I have some around, I've read that people have used it inside lenses without problems, and it's removable in case it fails. I let it sit out on some scrap plastic for a few minutes first to harden into more of a gel first.

I made some little tabs from masking tape, slid the tape under the the rim, painted a few drops in between the tape and rim with a toothpick, and then pulled the tape mask off before it hardened completely. This worked for keeping the lacquer completely underneath the little rim, and protecting the rest of the lens from accidental drips.

Seems like it worked: the glass no longer wobbles! I'll give it a couple of days to fully set and offgas before reassembling.

 

[Steve906]

Helge has a good point about expansion and air exchange if this is not provided by other means in the lens design.

 

[mrmekon]

This solution definitely isn't air-tight, but thermal expansion might eventually break it loose again. Luckily, it's incredibly easy to disassemble this lens.

I'm more worried about outgassing, since there's very little information about what adhesives are safe. I've seen some reports that "crazy glue" sometimes irreversibly hazes glass? Otherwise I would have used my "loctite extreme", which is flexible when hardened.

 

[xkaes]

Congrats!!! Always nice to see someone FIX something instead of throwing it away.

 

[BobUK]

As Helge said "Totally reversible," . That should be the way to go. I don't like repairing certain things so solidly that they cannot be corrected or disassembled at a later date.