Surprise find today - a Leica Hektor 28mm f/6.3 screwmount.
Description from Camerarepair.com: A 5/3 formulation with the outer pairs cemented and the rearmost pair larger than the forward pair. The 2.8cm F6.3 Hektor was introduced in 1935 to counter the 28mm F8 Tessar which was already available from the other optical titan, Zeiss, for its Contax. Until 1937, available in chrome or nickel finish. Thereafter in chrome only. Post war available with coated optics. Discontinued 1955.
Robert Jagitsch informed me that these lenses are difficult to find w/out haze so I think I lucked out big time. The lens is surprisingly punchy with no visible haze or CA. Exceedingly sharp and detailed in the center, I consider this a character lens so can forgive some apparent deficiencies in the corners. Then again, I've only shot it wide open (heh heh, at f/6.3), stopping down might improve.
This beauty is super compact with smooth focus. I'm using it with the Hawk's adapter so close focus is possible with nice separation. I think this one is a keeper.
Any color bleed or vignetting was added in post. I have not noticed any significant corner issues. Just some light vignetting at f/6.3. Sorry for the uninspired samples, just some very quick grabs - will update with some more later.