Archived posting to the Leica Users Group, 1998/01/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]In a message dated 98-01-19 10:59:17 EST, you wrote: << Subj: Re: [Leica] Why no ASPH teles? Date: 98-01-19 10:59:17 EST From: TEAShea@aol.com (TEAShea) Sender: owner-leica-users@mejac.palo-alto.ca.us Reply-to: leica-users@mejac.palo-alto.ca.us To: leica-users@mejac.palo-alto.ca.us Mark, I believe that the benefits of aspherical elements is more important with wide angle lenses than with longer focal length lenses. The opposite is true for low dispersion glass elements - they are more important in longer focal length lenses. This is apparent in other lens systems as well - Canon and Nikon particularly. >> I think TEAShea is correct. For longer lenses, the spherical (sections of a sphere) lens elements can be designed to optimize the image, especially when using glass having different optical properties, specifically refractivity. With long lenses, the optical paths of all light rays are not too far from being parallel to the axis of the lens. But for wide-angle lenses, the light paths must bend sharply, both coming into the lens at the front and, especially, exiting the lens at the rear. Making the front and rear lens elements aspherical (not spherical) results in the improvement. Charlie