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recementing a lens
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PostPosted: Sun Sep 17, 2023 12:26 am    Post subject: recementing a lens Reply with quote

looked through the history and not much on this topic.

Has anyone here sucessfully recemented a lens? What product did you use?

I picked up a nice vintage 5 3/4" F 2 ish bausch and lomb projector lens but one element is decemented. Easy to get into.

Wondering if it would work air spaced? e.g. touch but not glued?

Havent taken it apart yet, looks pretty easy.

unfortunately looking at Summers website, minimum is $50 plus shipping, dont need 4 oz which will go bad long before I use it.

PostPosted: Sun Sep 17, 2023 1:12 am    Post subject: Reply with quote

I have recemented one lens, a super yashinon second tier F/2.8 135mm lens. I used a commonly available epoxy glue advertised as being optically clear. It worked okay, but you need to make sure to remove all bubbles or air pockets, and careful that the glue thickness is completely even, and that you have aligned the two elements correctly. I don't know if I'd try it on something expensive.

Another time I didn't split the doublet, although I soaked it in acetone to begin the process of splitting it. Soon, I noticed the separation was gone. I think what happened was the acetone made the balsam run and spread out, so I added weight to the doublet to add slight pressure while any remaining acetone dried out. I had to do it twice but after the second time drying the separation was gone. I haven't rechecked that lens lately to see if the repair was good and permanent.

The first time I ever tried to split a doublet I used low heat, but there was the tiniest of flaws in one of the elements, it turned into a much bigger flaw. So you need to be careful.

PostPosted: Sun Sep 17, 2023 11:12 am    Post subject: Reply with quote

As Alun alluded to, separating the doublet may be the bigger challenge.

If the doublet has been cemented with Canada balsam, then gently, slowly warming it to about 300˚F / 150˚C should allow them to slide apart. I have had success with that on an older Minolta Rokkor lens.

I have a Bronica PS doublet with a hazed epoxy cement layer; soaking the doublet in acetone did nothing, methylene chloride is unobtainable here, the final option to try (according to Norland) is to gently heat the doublet up to 400˚F, and hold it there for an hour, upon which the epoxy should lose its adherence. I haven't had the courage yet to do that.

As far as cementing is concerned; a UV-curing optical cement can be used, or Canada balsam. I have had partial success with a UV-curing cement, but that was a generic one; optical grade UV-curing cements are difficult to source here, are very expensive, and have no shelf-life to speak of.

I do have a Canada balsam-in-xylene solution prepared for cementing; that requires a few weeks of edge-hardening before it can be handled.

Pure Canada balsam (not in hardened stick-form) can also be used, which can be made up of different hardnesses depending on how much of the natural turpentines you boil off before you use it. This type of Canada balsam cement needs to be applied hot, which isn't an easy task. Smaller lenses can use a harder balsam, larger lenses need a softer balsam.

Mounting the lenses with an air-gap is problematic if they were designed for cementing; you will need a very thin separator otherwise you will end up with Newton-rings. Oil-mounting would be another alternative, but I have no experience with that myself.