Archived posting to the Leica Users Group, 1997/05/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Bill Grimwood wrote: > > >[2] All three lenses, as well 500/8's by Minolta, Leica, Nikon and my > >1000/11 Celestron all focus to beyond infinty. Does anyone where know the > >reason Mirror lenses do not have an infinity stop? > > > > I believe this is due to temperature changes, the mirror can change size > due to contraction or expansion and this will cause the focus to shift. Some long lenses allow the user to focus beyond infinity, thereby enabling one to ensure that proper focus has been achieved. Someday, you may wish to compare the image quality of a mirror lens to that of an all glass lens. Many years ago, Walter Heun of Leica showed 2 slides side by side taken with the two different lenses. The color transmission of the all glass lens was far superior to that of a mirror lens. Hence, I now lug around the 400 and 560 lenses (plus a 1.4x extender). Mirror lenses also have other disadvantages - a high, fixed f stop and the potential of donuts in the highlights. To me, the superior image quality of an all glass lens offsets its extra bulk and weight. Bill