Minolta M-Rokkor 40mm f2 for Leica M brand_Calumet but it's obviously something else:

but it's obviously something else: one end has a standard 3/8" thread

and a range of magnetically-attached apertures instead of the original's somewhat awkward rubber-washer-and-insert system

It also works as a standard adapter

but it's pretty cool

Minolta M-Rokkor 40mm f2 for Leica M brand_Calumet but it's obviously something else:The Minolta M Rokkor 40mm f2 is tiny really tiny. It's barely 2cm long and as wide as the M mount at its widest point, making it an ideal everyday lens if you don't like bulk. The 40mm focal length is excellent for both full frame and crop bodies, and the f2 aperture is impressive for the size. Anyway, big fan of this lens. Fairly typical light internal haze, minor dust, neither of which materially affects imaging. Smooth focusing, good diaphragm,