Archived posting to the Leica Users Group, 2005/11/12

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Subject: [Leica] OT: which enlarger lens
From: red735i at (Frank Filippone)
Date: Sat Nov 12 06:15:24 2005

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

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.

In reply to: Message from richard-lists at (Richard) ([Leica] OT: which enlarger lens)