Archived posting to the Leica Users Group, 2005/11/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Most consumer lenses that say APO are not truly APO. I forget all the technical details, but basically there are 3 color frequencies they measure. If you get close enough that those 3 are in focus at the same distance from the target, then the marketing types label the lens APO. Truly, the most strict definition of APO is that ALL colors will focus at the same focal plane at ALL lens to target distances. Few if any lenses achieve this. It is usually true over a limited subject distance or over a limited color wavelength selection. Frank Filippone red735i@earthlink.net I did a lot of googling and book flipping lately so I forgot where I read it, but someone did say that most APO enlarger lens are not true APO since they don't have the apochromatic thingie.