Quote Originally Posted by cowanw View Post
I wonder if something like a Imagon set of adjustable holes would be usefull?
They would work more like Waterhouse stops, but they would work. The Imagon apertures were designed to allow differing percentages of abberations from the outer parts of the lens to affect the image for controllable softness. Modern mirror lenses won't have much of this present, and mirror lenses don't have the same chromatic aberration of refractive lenses when properly made.

With the focal lengths typical of these lenses, f:8 isn't nearly hyperfocal, and many people use these lenses for closer photography, like birding from a few meters away.

Lee