The Spiratone 500mm f8 Minitel-M is a mirror lens, packing high magnification into a relatively compact package with you know, a few tradeoffs. Donut-shaped bokeh is one; the reality of controlling camera shake and focusing a 500mm lens is another. But none of those are the end of the world, and its nice to have this kind of reach in a package about the size of a coffee cup. Included is the matching Spiratone Plura-Coat 2X Tele-Verter (7E), which screws right in to turn this into a 1000mm lens. Amazing! A revolution! Whats that youre asking? Whats the F stop with the Tele-Verter? Ha ha, good question, you see, its not really important when you consider that whats that? You actually want to know what the f stop is? Ha ha the thing with teleconverters is, every, uh, ha ha, look over there its f16.This is a T mount lens and can be adapted to many different mounts. It is supplied with a Minolta MD mount.