Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP Path: utzoo!watmath!clyde!floyd!harpo!decvax!decwrl!dec-rhea!dec-nermal!hagerman From: hagerman@nermal.DEC Newsgroups: net.rec.photo Subject: lenses Message-ID: <1545@decwrl.UUCP> Date: Fri, 15-Jun-84 11:13:58 EDT Article-I.D.: decwrl.1545 Posted: Fri Jun 15 11:13:58 1984 Date-Received: Thu, 21-Jun-84 03:13:06 EDT Organization: DEC Engineering Network Lines: 27 x re: lenses sharpest at medium f/ stops. If you don't think it's possible to build a lens that is sharpest at its widest opening, consider this: My lens is sharpest at, say, f/8. I put a mechanical stop on the aperture (note spelling) control so that it can only move between f/8 and, say, f/16. Now I have a lens that is sharpest at its widest opening. If this sounds far-fetched, try measuring the diameter of the front element of some of your lenses and then calculating what the maximum f/ stop should be. You'll find, in many cases, that the front element is larger that you would expect. (Specific example: Leitz Summitar 50mm f/2.0 works out to about f/1.5.) This is to minimize vignetting problems. The manufacturer can choose between making a lens that is faster but not quite as sharp or a slower lens that is sharper. In fact, Leitz claims that their 50mm f/1.0 is as good as their 50mm f/2.0 lens. The problem is that the f/1.0 lens is a monster. The point is that lens design, like a lot of other things, involves compromises, and the result is that most lenses are sharpest at medium f/ stops. D. Hagerman