ClearView 300mm f5 Multi-Coated Mirror Lens w/ Aperture Ring for M42 -Clean-
This is a fast 300mm mirror lens that could fit in your pocket. I haven't seen mirror lenses with aperture rings before, the ClearView allows you to stop down from an f5 through f11.
It is in excellent condition with light wear and works perfectly. The glass is clean and scratch-free with no haze, fungus or other problems. The focus and aperture are smooth.
Lens caps and a rear mount UV filter are included along with the nice metal lens shade.