What is this lens - SEMMAR Y.O. 300mm F5.6 in copal 3 ?

[koh303]

123131

I bought this lens as a learning tool for #3 shutters. It came with a stuck shutter, which has since been CLA'd (by me), however i cannot find any info about this lens.

It appears to be a basic tessar design, though i am not sure there is such a thing as a tessar 5.6 300mm...
It coveres 8X10 at infinity as far as i can tell but have not checked how much movement it offers if any.

Can any one shed any light?

[karl french]

Perhaps another variation of the Congo/Osaka Commercial series of the lenses.

[koh303]

i haddent considered that - however - the congo is 6.3

[Tracy Storer]

Interesting. A quick search finds reference to TLR cameras with 75mm Semmar lens, made in Paris. Yours says Japan. You think it's a Tessar type based on # of reflections,etc?
Congrats on the CLA.
Curious how the lens will perform?

[Paul Ewins]

Just guessing, but perhaps Y.O. stands for Yamasaki Optical. There is no mention on the camerapedia page of an f5.6 lens: http://camerapedia.wikia.com/wiki/Yamasaki in their range however. f5.6 is usually associated with the plasmat design and the Schneider Symmar is a plasmat so I would guess that whoever sold the lens was hoping for confusion/name recognition.