KK> Many thanks for the very detailed answer. Can you elaborate on the KK> passage above a bit, please: what do you mean "covers much larger KK> image circle"? Are you using a Pentacon 6 lens? I was think M42 KK> implementations.
Lenses have an circle of acceptable* coverage, that is inherent in the lens design, and doesn't change with focal length. (*: acceptable means that the image is still usable, while the lens might still show more of the world outside this circle, it will be too much blurred or darker to be usable). For example, the 2.8/180mm Sonnar design has an angle of coverage of about 30 degrees. When scaled to 50mm lens, it will still cover just 30 degrees, the same when scaled to 300mm lens. The 1.5/50mm Sonnar is somewhat different design, made to cover ~50 degrees, thus making it a normal lens. 30 degrees with 180mm lens means that the 6x7cm film area still fits in the circle produced by the lens (if not obstructed by internal baffle or the lens barrel). The Olympia Sonnar, the 2.8/180mm was originally produced for Contax rangefinder camera (which could still focus a 2.8/180mm lens at longer distances like sports somewhat accurately!), but it was made so it covers even medium format film with ease. The second version (black, with large protruding tripod foot, pre-set aperture) actually had unscrewing rear mount which you could exchange for many other mounts. The third version, sold as 6x6cm lens for Pentacon 6, is still optically the very same, just in a barrel for P6. Longfocus lenses (whose physical length is the same as their focal length) often do have much larger coverage then the telephoto type lenses of same focal length (telephoto types have much shorter physical length then their focal length, extreme example is the mirror lens, which is 500mm focal length but much much shorter physically). Some longfocus lenses for 35mm film were often adapted for larger formats. However, the 2.8/200mm CZJ lens, is made specifically for 35mm film, and has (supposedly) less coverage. Anyway, one would have to change the barrel to avoid vignetting on larger format. >> If you are interested, I can send you a file from my 6MP DSLR shot >> with the 2.8/180 Sonnar. KK> Yes please :-) I will try to find a good one, at low ISO. Focusing that lens on APS dslr is a little hard (the Nikon has pretty bad viewfinder). Best regards, Frantisek Vlcek
