Cementing Lens elements?

[Ned.Lewis]

Hi All,

I've read the book Primitive Photography, and am thinking about trying to make my own duplet lens using a pair of identical achromats. Surplus shed sells lenses that might work but the achromat pair is separate crown glass and flint glass and not cemented. There is a comment on the page that says something like "don't worry we sell balsam too" but I'm not so sure about the idea of cementing the elements together myself and I don't know what "balsam" is or how it would help!

Right now this whole thing is just in the mulling over stage, but I'm curious to know if this is something to avoid.

Thanks!
Ned

[Tom Persinger]

Hi Ned-
I've purchased those lenses from Surplus Shed before and used them without cementing. It probably isn't ideal, but to be honest the image looked great... That said, Balsam is usually Canadian Balsam. It's made from the resin of fir trees and is often used to cement lens elements together. I haven't tried it, but from what I understand you put a big dollop on the center of one lens and then push the other down on top of it with even pressure so that it slowly squeezes the balsam evenly between then. Let it dry and voila!

Disclaimer: the above (re: cementing) reflects my understanding, and may not be correct

I have a nice big vial of canadian balsam here, but haven't cracked it open... let me know if you proceed!

[Ned.Lewis]

Thanks Tom! If they can be used without cementing, that sounds fine to me. I didn't know how precise the registration between the two lens elements needs to be. Anchor optics also sells cemented achromats for a little bit more, so that's an option. Also it occurs to me that the lenses from surplus shed are so inexpensive that there's not much risk in trying the balsam!

[Tom Persinger]

agreed re: inexpensive experimentation! If you try it, let me know how it goes... or better yet, take some pics and post here for all to see! thanks!

[Ned.Lewis]

Thanks Tom, I will!

[Randy]

Resurrecting an old thread, but some might find my experience interesting.

I cemented a pair from surplus shed with a super glue that was designed for glass - I no longer have the tube as it dried out so I can't recall the specific designation.

A couple years ago I got an old brass barreled lens, probably a rapid rectilinear, that had bad balsam separation in one element pair. I removed the pair, soaked it for a week in acetone to separate them - worked fine. I didn't want to screw them up trying to re-cement them together so I put a drop of canola oil between them and pushed out any bubbles by applying pressure, put the lens back together and shot with it for the next six months until I sold it (of course disclosing what I had done). After six months the lens pair with the canola oil was still crystal clear. I am sure at some point the oil would dry out or discolor and it would have to be cleaned and another drop of oil put between them...but it worked great.

[Ned.Lewis]

Thanks that's good to know.

This thread was more than two years ago, and I managed to fill some notebook pages with doodles but never made a lens! Got to bump this back up the list.... it still sounds like fun.

[Tom Persinger]

i love it when these old posts find new life with new information. Thanks for sharing your experience Randy! Keep us posted Ned!

[Jim Jones]

One of the main reasons for cementing lens elements that have an exactly mating curve is to eliminate reflections. Each air-to-glass or glass-to-air transition of light in uncoated lenses causes about a 5% reflection. This reflected light can cause flare and reduced shadow contrast on film. If the mating surfaces are cemented with something with close to the same index of refraction as glass, these reflections are nearly eliminated. Modern lens coating decreased the need for designing lens elements that could be cemented together, freeing the designer for making higher performance lenses. Photographers who are satisfied with pinhole and primitive lens performance may be content without lens coatings or without cementing lens elements where possible.