What is this???? Contax lens oddity

[wlewisiii]

Saw this in a post on beststuff and thought maybe someone here might have a clue.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3867290793&fromMakeTrack=true

William

[rover]

Enlarger lens I bet

[Doug]

I does sorta look like a Contax RF mount, doesn't it. I didn't know enlargers used that mount, but could be; most all I've seen are Leica 39mm thread. The description text missed the "5"... Lens ring says F=5cm, so it's a 50mm lens. No mention of max aperture...

[Brian Sweeney]

An enlarger lens usually has an F-Stop adjustment. This looks like the kind of lens used in a Lab for copy work or recording instrumentation.