I have a Soviet made 500mm mirror lens that came with four filters, three of them are easy to figure out.
One is amber, one is green, and one is gray.
The fourth is the one I am not 100% sure of, its clear so my guess is that its a UV haze filter but sometimes its better to ask.
There does not seem to be a brand name on the lens, but it does have what I guess is a brand mark/symbol. A lower case 'c', inside a triangle, inside a circle.
The only marks on the filter are:
*CIO <the_brand_mark> 77x0,75
So am I correct in thinking that its a UV haze filter, or is it something else?
Possibly just a piece of glass to help protect the lens?
Or a super secret filter used to view invisible inks on KGB documents?
It was made during the 'Cold War' (1979)
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