SCHNEIDER/KRAUZNACH 75MM 3.5

anthonym3 · Jul 31, 2023

The lens has pinpoint opaque dots throughout. It appears to be between elements, does not display the spider web fungus appearance. Does anyone have an idea what it may be?

JPD · Jul 31, 2023

Are they between the first and second element or on/inside the back lens group? (Assuming it's a Xenar). Is it a unit or front element focusing lens?

It could be deposits from evaporated lubricants, bad Canada balsam/separation or coating damage (if the lens is coated).

anthonym3 · Jul 31, 2023

Sorry, it is a XENAR. It's on a ROLLEICORD, the coating is clean no loss. It's probably between elements. There is no fog. Might it be usable for black and white with a lens hood?

JPD · Jul 31, 2023

It shouldn't be too difficult to unscrew the lens and try to clean the surfaces. The front lens assembly should be easily unscrewed from the shutter with a rubber friction tool. Then you can unscrew the second element. Don't unscrew the front element retaining ring as it isn't necessary.

anthonym3 · Aug 1, 2023

I've done that. It appears the dots are between cemented elements. There is no hint of balsam separation but could this be the beginning of it?

JPD · Aug 1, 2023

anthonym3 said:
I've done that. It appears the dots are between cemented elements. There is no hint of balsam separation but could this be the beginning of it?

Yes, sadly, it's a problem with the balsam if the dots are inside the cemented pair. Since the back group is the one with the highest power in the lens and focuses the image on the film the dots will probably affect the image quality more than if they were on the front element.

JPD · Aug 1, 2023

Maybe @Nodda Duma knows more about this problem.

I also have an old lens with white-ish dots between two elements in a group of FOUR cemented elements (a Rietzschel Linear) and it's pretty much unuseable because of it.

SCHNEIDER/KRAUZNACH 75MM 3.5

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