Archived posting to the Leica Users Group, 2012/11/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>From a 2006 email from Bob Salomon, an employee for a long time at HP Marketing..... "The Apo designation for large format taking lenses and photographic enlarging lenses is "that the lateral chromatic aberrations of the secondary spectrum have been correct to within a very small percentage of the focal length". The Apo designation for lenses used for microscophy is the traditional Abbe definition where "the primary color rays cross at a common point". This is also the common definition. " See, no actual wavelengths are stated..... Frank Filippone Red735i at verizon.net -----Original Message----- From: lug-bounces+red735i=verizon.net at leica-users.org [mailto:lug-bounces+red735i=verizon.net at leica-users.org] On Behalf Of Frank Filippone Sent: Saturday, November 24, 2012 3:58 PM To: 'Leica Users Group' Subject: Re: [Leica] So, wouldn't a 50mm Summicron LTM or 35mm f2 ASPH LTM be the best enlarging lens on earth? Physics.... White light is composed of all the colors. B+W Paper has a spectral response. If you want the theoretical best you can do, then you need to either shoot light at the paper from a single wavelength or second best, make sure all your wavelengths are focused at the same plane (negative stage). Definitions of APO vary..... all over the place... 3 (unstated ) wavelengths, 4 ditto, from x to y nanometers, etc. There is no scientific definition, AFAIK. Frank Filippone Red735i at verizon.net Does an apo lens bring all three primary colors to the same focus point, as opposed to just two out of three for a non-apo lens? If that is the difference, why would an apo lens offer any advantage for B&W printing? _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information