white spots = Dreaded Killer Fungus(tm) ?

Hi everyone,

over the holidays I bought a used Sinar p with several lenses. Two of them (symm ar-s 5.6/210 and symmar-s 5.6/150) show small white dots on the black metal part between the first two lenses (when looking through the front lens ). AFAIK ther e's nothing on the glass itself, just the metal. The whole thing looks very diff erent than what Toomas Tamm shows on <http://www.chem.helsinki.fi/~toomas/photo/ fungus/>, nevertheless could this be some sort of fungus?

side view diagram:

-------- /* | | / | | * = small white dots --- | | | | | | | | | | | | | | | | | | --- | | * | | * | | --------



If it would be helpful, I probably could provide a link with pictures.

Regards, Christian

my little diagram didn't survive...

the correct ascii-art can be found at: <http://n.ethz.ch/student/chrsigg/fungus.txt>

regards, christian

argh!! feel like complete idiot. put url in brackets, interpreted as html, got killed. link is at:

http://n.ethz.ch/student/chrsigg/fungus.txt

(is there a way to preview/edit your posts?)

This spotted appearance of the elements is common in older Schneider lenses. The phenomenon is due to voids/defects in the paint on the edge of the lens. The element looks good and the paint appears perfect.

I don't know what, if any effect this has on the optical performance. It sure reduces the selling price however. Its really easy to make it much worse and is probably best left alone. To repair involves removing the paint from the edge of the lens, cleaning the glass and applying a good adhereing opaque black paint to the angled ground edge of the element. This is done at the factory by skilled workers using a potters wheel sort of thing and applying the paint with a brush as the element is spun at about 100 rpm.

It takes a lot of practice to get this right and its not a simple matter of "what's the secret paint?" I can do this work and rate it at about a $125.00 job for one element or about $200.00 if front and back done at the same time.

Skilled amateurs should practice on junk lenses to experiment and perfect their techniques.

However it's hard to add something after SK Grimes, you may have a mook at my page :

http://www.multimania.com/cesarigd/photo2.htm

(in French), showing a photograph of fungus and an enlargement. At the bottom of the page, "champignons sur les lentilles"

Because it's such a common problem on Schneider lenses, I've heard this called Schneideritis! I've pretty much standardized on Schneider lenses from the 70's, and I see quite a bit of this problem in looking for lenses. Schneider has said that this defect will not affect image quality. But, I wonder. If there's going to be internally reflected light, then there's going to be some amount of flare from those little hot spots inside the lens.

Given that this problem is much more common on Scheider lenses, versus Rodenstock or other lenses, it appears to be preventable. Yet, I was surprised to hear of a case where this problem occurred on a more recent Apo-Symmar lens.

Thank you very much for your insightful answers.

Christian

Both my Apo-Symmar 150 and Super-Symmar 110 XL had some when I bought them new. I sent them back under warranty but was told everything was alright. Seems to be considered as a simple cosmetic flaw.

I don't believe that this condition is confined to older Schneider lenses. I have a 47XL the rear section of which displays considerable 'infestation'.

A friend just shelled out for a Super Symmar XL 210mm and is sending it back due to the marking.

Walter