> One thing that I don't think has been mentioned about mirror > lenses, is that the bokeh tends to look like little round donuts, > due (I suppose) to the little round mirror (or whatever it is) on > or near the front element of the lens.
Although the "donut bokeh" got a lot of mention in this thread, there is another shortcoming that many (but not all) mirror lenses have, and that's what is sometimes called a "mirror lens hotspot". This refers to the fact that many mirror lenses (and the original Russian MTO was one of the worst offenders in this regard, I guess) are guilty of a lot of light falloff toward the edges of the frame (so that the center sometimes seems a lot brighter, hence the "hotspot"). However, some mirror lenses seem to be less prone to this than others, and, of the four K-mount mirror lenses that I have right now, I think the Pentax has more light falloff than do the other three. Fred
