Oh no. It’s this one.
http://www.bythom.com/300lens.htm
I picked up a (Kenko) teleconvertor for it, but it changes the lens from being a ecstatic joy to use into a so-so “420 mm” f5.6. A damn shame.
Never messed around with mirror lenses.
A 1500mm f4 must be crazily wide.
