In the process of writing the my last message on this I left a space for the title of a book by Warren J. Smith, expecting to add the title later, after I looked it up. But I forgot under the pressure of time and so I write again. The title of the book is "Modern Lens Design". However, contrary to what I wrote, the optimum when ONLY spherical abberation is considered is an unsymmetrical double convex lens. The trouble is that this yields a lot of field curvature and it so a little more spherical abberation is tolerated with a meniscus chosen to have low field curvature in a simple camera. The deign is known as the Wollaston simple meniscus and it has the concave side facing the subject to be photographed. The value of the design can be seen in a pair of photographs in "A History of the Photographic Lens" by Rudolf Kingslake. At the center of the images the double convex lens produces results as good (and probably even a bit better) than the meniscus, but away from the center the meniscus soon looks far better when the image is made on a flat film. As I recall the original question in the thread, the application was to use a 40 to 50 mm lens to photograph on a 6x6 frame. This is already a wide-angle application and the issue of field curvature will be especially important, making the DCX look particularly inferior. In any case, at this wide an angle, a multiple element lens is probably worth looking for unless the outer portions of the image can be a little out of focus (sometimes desired in a portrait, but rarely does one want to make a serious portrait with a wide-angle- it makes the nose look too big!) Already a two element lens brings massive benefits (the Hypergon is an extreme example but though the design is old people are still making them and they bring impressive prices, yet they have only two elements of the same glass and are not even achromatic.) Bob Mueller Dr. Robert Mueller Institut für Festkörperforschung, FZ-Juelich D-52425 Juelich, Germany phone: + 49 2461 61 4550 FAX: + 49 2461 61 2610 email: [EMAIL PROTECTED] _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
