I've heard of people cutting diaphragms of black paper to increase DOF on mirror lenses. Ain't something I'm ever going to mess with, though. And I used the built-in ND filters on one of my mirror lenses for exactly _one_ shot so far; I could certainly live with a mirror lens that left this feature off.
-Lon T Rittenhouse wrote: > > Reflex lens: Light comes in though a lens element at the front, is reflected > from a donut shaped mirror at the back, to a round mirror at the front, > which reflects it back through the hole in the rear mirror to a lens group > at the back, and then onto the film. In other words it is a reflector > telescope with a camera mount. > > Very short due to the folded light path. Very light due to being mostly air. > A diaphragm will not work in one, so the only way to adjust light > transmission is with ND filters. There is no adjustment for DOF. Filters are > usually inserted at the back of the lens as the front is very large in > diameter. Out of focus highlights form a characteristic donut shape that > some people dislike immensely. > > If you don't know what one looks like go down to your local camera store or > science hobby store and look at a small reflector telescope. Imagine it with > out the viewing lens and mount. > > Though there have been some shorter ones they are usually 500mm and longer. > Their popularity began with the very inexpensive Russian import MTO that > Spiratone sold back in the late 60's though Zeiss had one for the Contarex > long before that. > > Ciao, > Graywolf > http://pages.prodigy.net/graywolfphoto
