Archived posting to the Leica Users Group, 1998/04/29
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Bryant, > Marco is correct. IF you take a picture with a 50mm lens, take it off and > put on at 35mm lens from the same spot and take another picture then > compare them by masking off the parts of the 35mm print that is not in the > 50mm print you will see that the two match. Almost completely true but there are design elements which kill the generalization. Peripheral apparant perspective distortions appear when a given focal length is lengthened or compacted, in terms of its back focus requirements. This is most commonly known as the telephoto effect but applies to the rendition of retrofocus wides vs. symmetrical wides as well. And, for the generalization to hold completely true, the crop would have to be centered on the optical axis (off axis enlargements/crops of a wide photo will still show a stretched perspective). Small pocket cameras, with their telephoto normal/slightly wide lens designs are the best example for proof of the effect. A camera like the Olympus XA, while having a 38mm (I think) lens, has more peripheral 'wide angle' distortions than a Leica CL's 40mm because its angle of projection is more extreme, which produces a heightened wide angle effect, off axis. Retrofocus designs provide 'extra' back focus relief and so, relax the projection angle, which reduces the 'wide-angle' effect produced off axis, on film. Regards, Danny Gonzalez