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White dots on MC layer phenomenon...?
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PostPosted: Wed Jan 28, 2009 12:45 pm    Post subject: White dots on MC layer phenomenon...? Reply with quote
Some time ago, I find out, that some lenses (and it's really typical only for specific lenses) have ultra-tiny white dots on inner coating layers. These dots don't change in time, they don't seem to be related to fungus, because any single lens showing these dots hasn't any sign of fibres or tree-like marks of fungus and these lenses even doesn't smell stuffy, like many fungused lenses smell. They doesn't impact optical performance and in most cases are only barely visible.

I've been told, that these dots are just symptoms of age of some kinds of coating layers and it isn't cleanable. Another source told me, that this can be caused by change of temperature, resulting condensation of water droplets and their desiccation.

I've seen this dots repeatedly on 55mm Revuenons and 135mm Jupiters.

Here is 100% crop from very close-up shot:



Any ideas, what can cause it?


PostPosted: Wed Jan 28, 2009 5:00 pm    Post subject: Reply with quote
It happens on some Minolta M lenses too - I think it may be something to do with the cement they used?


PostPosted: Wed Jan 28, 2009 5:03 pm    Post subject: Reply with quote
That's erased coating.
Jupiter-37 is well known for having a very thin easily damageable coating.


PostPosted: Wed Jan 28, 2009 6:43 pm    Post subject: Reply with quote
That sounds plausible, but how can be the coating of inside surfaces damaged, while the outside coating is intact?


PostPosted: Thu Jan 29, 2009 3:28 am    Post subject: Reply with quote
I think this is what is commonly called "Schneideritis," because it often affects lenses made by Schneider Kreuznach. This has nothing to do with fungus and has very little or no influence on image quality. Please refer to this thread: http://photo.net/large-format-photography-forum/00K3xH

Cheers!

Abbazz


PostPosted: Thu Jan 29, 2009 11:42 pm    Post subject: Reply with quote
1. Might be condensation. If a lens is used in the cold and then brought inside, this phenomenon occurs. A good cleaning usually rectifies the issue.

2. Might be oil condensation. If the lens is not used for a long time, or if it's used in hot conditions, oil can evaporate and then condensate on the glass. I've seen this happen to one of my Jupiter-37 copies. Depending on how long ago this has happened and of what type of oil is used, this may be possible to clean. My J37 still shows traces of it on the coatigs of the rear element yet they don't affect the image.


PostPosted: Fri Jan 30, 2009 12:21 am    Post subject: Reply with quote
Abbazz wrote:
I think this is what is commonly called "Schneideritis," because it often affects lenses made by Schneider Kreuznach.


No Schneideritis. That looks like element separation limited to circular segments along the outer area of the lens - actually it merely is separation of the black lens rim lacquer, and as such, it is fairly easy to fix yourself.

These dots positively are condensation - which in its turn may cause a secondary coating damage on soft-coated lenses. Either directly by dissolving the coating, or indirectly whenever the lens is improperly cleaned.

Sevo


PostPosted: Fri Jan 30, 2009 3:02 pm    Post subject: Reply with quote
I had one filter skylight and a lens 135/4 voigtlander with this problem.

The filter was an colored acetate ( very strong rose) between two crystals.

Not matter this to me.

Rino.
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