Diameter of the opaque spot on original Thambar 48mm filter?

[1234]

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I am assisting someone with selling off remainders of the collection of an esteemed former president of LHSA. She has an old Thambar in user condition without the filter having a central blocking disc. I have found an old Leitz 48mm UV filter of that vintage and want to paint the requisite patch in center of the glass so as to evaluate the lens. Could someone tell me the particulars such as diameter of the opaque section, whether it is "solid" or on just the inner or outer surface, and anything else that might assist. I understand the new version is 49mm but presumably same patch. Thanks, Harry in Florida

[luigi bertolotti]

Diameter is 14mm (on my one... supposedly original) , surely applied onto the inner face (towards lens) , matte black the inner face, silver (not matte - it's like a small mirror) the face visible from front. The glass in itself doesn't look an UV filter, though, but simply clear glass. The external diameter is black and finely knurled - no writings

A pair of good pics (of a declared original) here : https://www.leicashop.com/vintage_de/leica/leica-screw-mount-lenses/thambar-2-2-90mm/leica-thambar-2-2-9cm-sku32407-1.html   (my one looks like, but the front surface of the spot is definitely REFLECTING, not opaque like in the above pic... but who knows the image processing... ) ; my feel is that the spot looks applied ("glued" ?)  - not painted onto, and not some odd "treatment" of the glass (front surface looks "untouched")

 

Edited September 7, 2020 by luigi bertolotti

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[kangaroo2012]

 I have 2 Thambars, one has a filter spot closer to 13mm the other 14mm in diameter.

One is quite silver on the outer side the other takes a lot of moving around to see the 

silver finish.

Both are applied spots , one is starting to ripple as the lens has been through a tough life.

Hope this helps

Cheers

Philip

 

[1234]

Luigi and Philip, Thank you both in Brescia and Sydney for the helpful information. I am guessing that the surfaces are flat and that the silver patch is perhaps also on the inner side of the glass, a sandwich with the black patch. Only reason I could imagine for use of the silver would be to scatter a few more incoming photons across the surface, or within the glass, of the filter to enhance the dreamy effect?? If the silver were on the outer surface, how could it have any effect on the film/sensor?

[luigi bertolotti]

9 hours ago, 1234 said:

Luigi and Philip, Thank you both in Brescia and Sydney for the helpful information. I am guessing that the surfaces are flat and that the silver patch is perhaps also on the inner side of the glass, a sandwich with the black patch. Only reason I could imagine for use of the silver would be to scatter a few more incoming photons across the surface, or within the glass, of the filter to enhance the dreamy effect?? If the silver were on the outer surface, how could it have any effect on the film/sensor?

That's my opinion too... the reflecting surface behind the clear filter glass someway increases the desired "confusion/softness"

Edited September 10, 2020 by luigi bertolotti