why do elements seperate?

msbarnes

msbarnes

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do they just do?

I ask because I'm interested in acquiring a tele-rollei; however, these are very expensive and lens separation are very common if I recall. I haven't looked into this topic before but if I wonder if a tele-rollei that doesn't show any signs of lens separation will still have a high chance of separating?

I'm specifically interested in the case of the Rollei but I post this here because I would like to understand this better since all lenses are susceptible to separation. I wonder if any extra precaution can be taken.
 
Okay, I hope the organic chemists will chime in, but, in the 50's, the optical cement of choice would be Canadian Balsam. The clue to separation would be to examine the aging and degradation modes of the Canadian balsam.

More modern lenses would be glued with UV curable epoxy, which becomes almost impossible to separate.

I found this url informative: http://www.atmsite.org/contrib/Sapp/LensGlue/

And from here: http://www.microbehunter.com/2010/01/23/an-overview-of-mounting-media-for-microscopy/

Canada Balsam: This is a natural mounting medium obtained from the e balsam fir tree (Abies balsamea). The optical properties are nearly identical with those of glass. For this reason, Canada Balsam was used for many years as a kit to hold optical lenses in place. Meanwhile, synthetic lens kits have replaced Canada Balsam, it is still used as a mounting medium for microscopy, however. Canada Balsam has the advantage that its optical properties do not deteriorate with age. Permanent slides mounted with Canada Balsam have been stored for a century and are still useful.


And I have personally separated and repaired de-cemented lenses, using the boiling water and methylene chloride soak.

Back to your question, yes, I think all balsam-glued lenses are susceptible to separation. I would think temperature cycling lenses (from cold to hot to cold and again) would accelerate the process. Stable storage would help prevent separation. I'm not sure how humidity would affect the balsam, but high humidity would be bad for fungus.

Hope this helps
 
Vickko said:
Okay, I hope the organic chemists will chime in, but, in the 50's, the optical cement of choice would be Canadian Balsam.
Click to expand...

Not really - Zeiss had already gone over to a three (later two) component epoxy prior to WWII, and in 45 the Zeiss patents went public domain so that just about every other maker followed up, except for Kodak, who had already started using UV curing cement in the war. If any, the mid fifties mark the time when makers switched from epoxies to UV curing cements.

Separation is somewhat inevitable as lenses are highly polished, so that cements must work purely by adhesion.
 
I was told by the owner of a lens company that the glass was badly fitted and that the cement was used to 'fill' too much, over time the strain of the element finally pulling apart caused the crystallization.


I'm more familiar with LF optics and Goerz lenses which are very well made rarely rarely have separation while many other makers lenses do.
 
oneF said:
I was told by the owner of a lens company that the glass was badly fitted and that the cement was used to 'fill' too much, over time the strain of the element finally pulling apart caused the crystallization.


I'm more familiar with LF optics and Goerz lenses which are very well made rarely rarely have separation while many other makers lenses do.
Click to expand...

Although I cannot dispute the comments you attributed on a general basis, I must admit I have a bit of difficulty translating them directly to the Tele Rollei issues which are well documented. Firstly, they're a Zeiss lens, and, whilst nobody's perfect, Zeiss quality control was usually pretty good at the time if you take a look at many of the other lenses they were making including those fitted to 2.8 Rolleis. Secondly, a good sample of the 135mm Sonnar from the Tele is capable of stunning image quality. I don't pretend to have any special knowledge of or expertise in optical cementing, however these two points don't really gel with problems emanating from poor assembly or substandard lens grinding do they? Which doesn't mean it's not possible, of course.

It's worth noting that some other Zeiss lenses from around the same time have the same type of fault. Occasionally a 2.8 Planar lens fitted to the TLRs will be found with separation (nowhere near as regularly as the Teles Sonnar). I'm a keen Contaflex SLR user, and it's not unknown for the optional Pro Tessar lenses to have separation problems also. The 85mm versions, in particular, are extremely prone to it, and it is the exception rather than the rule to find one with no separation at all, but the 35mm and 115mm Pro Tessars are not immune, either. My own 85mm f/4 Pro Tessar has a few small bubbles on the edge of the glass, but still performs very well despite this.

So if the root cause of the element separation that manifests itself in these older Zeiss lenses is as per your suggestion, Zeiss must have been guilty of sub standard assembly or loose tolerances in relation to several lens types, not just the 135mm Sonnar.

I was under the impression that deterioration of the synthetic cement used to join the bonded groups over decades was the root problem. This stems from discussions I've had with a motion picture lens specialist who is also a Contaflex user. As well as being a very competent lens specialist, he also separated and rejoined a Contaflex lens, and thus has first hand experience with some of the affected lenses. I recall him telling me it took weeks of soaking in Milsolve, before the Zeiss cement finally gave up its grip on the joint involved.

Of course some of the above is conjecture, but sevo's previous comments also echo my understanding that Zeiss were at the forefront in adopting synthetic alternatives to canada balsam (although I wasn't aware of the patent details). So I was simply of the understanding that the issues some of the tele lenses have now, is a consequence of Zeiss being the first in the field to move to synthetics. Naturally, I'd find any solid information about the issue to be of great interest, but I hope my comments assist.
Regards
Brett
 
'So if the root cause of the element separation that manifests itself in these older Zeiss lenses is as per your suggestion, Zeiss must have been guilty of sub standard assembly or loose tolerances in relation to several lens types, not just the 135mm Sonnar.'


Yes, Zeiss didn't make everything perfectly 'all' the time I think we can agree there. I have seen not one CZ Planar/Schneider Xenotar with the separation often that is often seen in the tele design and those lenses(Planar/Xenotar) were made at the same time, it may be that the actual design of the 135 was one that Zeiss didn't have enough practice making and as a result wasn't made well. Planars etc have been made in the tens of thousand, the 135mm tele not nearly as much. If the cement was the problem then 'all' their lenses would have separation but that isn't the case. Merely by being a Carl Zeiss lenses doesn't make it magical and perfect every time :)
 
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