Separation?

[John Conway]

I always do research before I ask the question here but the forum provides the best info . So , is separation a red flag when considering a lens ? What exactly is separating and does the separation continue to get worse with time?

[goamules]

Good question that should have a thread. Most lens designs cement or glue pieces of glass together. For more than a hundred years, they used Canadian Balsam to do this. Sometimes, the balsam becomes crystallized or otherwise starts to release. Often seen at the edges as a yellow ring partially or fully around. I wouldn't worry about this type. It does not seem to increase in a few years or even a decade, in most cases. I've got a lot of lenses from the 1850s that have a little edge separation. If that's the worse it can do in 160 years I'm not too worried.

Sometimes the lenses start to separate in the main part of the lenses, as a yellow or white or black spot or feather appearance. The latter indicates the separation might be growing. Either way, any obstruction in the center of a lens starts to reduce contrast and can be less than ideal. A small dot or two on a large format lens I wouldn't worry about. Large amounts that cover, say, 20% of the glass will be a problem. The solution is to re-cement them, an expensive repair unless you do it yourself. And few do.

How to prevent separation? The type, thickness, and application method varied between manufacturers. You won't see many Voigtlanders separated, for example. But you will see a lot of Gundlach Turner Reich that are. I also believe years in the hot sun, such as in a window display, or other temperature variations may contribute to separation. Finally, don't clean the edges of your glass with strong solvents, which can start to wick into the seam.

[Dan Fromm]

John, it depends on the separation. Three examples:

16/2.5 Luminar with balsam piled up around the periphery of the front element and major voids between the formerly cemented elements. The lens appeared to have been baked, front down. Less than half the resolution, by test, of a known good 16/2.5 Luminar and miserable contrast.

58/5.6 Grandagon with silver spots in the rear cell and rings of fire in both cells. This is a modern lens made with, alas, the wrong modern synthetic cement. Looks like hell, shoots quite well.

Kodak 25-15 converter for the 25/1.4 Cine Ektar II. I have one with magnificent Newton's rings that can be seen through my Beaulieu's finder and on footage shot with it. Completely unusable. I'm not sure what the cement is.

Garrett, watch what you say about Voigtlaender lenses. In modern times V used what seems to have been the same wrong synthetic cement as Rodenstock. I have a couple of Apo-Skopars with spectacular rings of fire in the drawer.

[goamules]

I'll watch out. You know about the modern stuff more than I do, I was thinking of old 1800s ones.

[Jim Jones]

I've used an inexpensive Symmar with edge separation. The images at small apertures are fine.

[Tim Deming]

I'll watch out. You know about the modern stuff more than I do, I was thinking of old 1800s ones.

The post-WWII Apo-Lanthars, Apo-Skopars, and small format 50mm Septon, are all highly prone to separation. These seem to be the only Voigtlander lenses affected by significant separation most of the time.

By the way, I have repaired a couple Voigtlander Petzvals with very bad balsam degradation (front lens of course)

cheers

Tim

[hoffner]

So , is separation a red flag when considering a lens ?

Separation can change elements alignment in a lens. I think you already know, what that can mean.