In article <5acvhe$89j@tor-nn1-hb0.netcom.ca>, rbbuck@netcom.ca says...

>Why are APO lenses better then non APO lenses. I have read that they have bett
>er contrast, and slightly better colour reproduction for longer focal lenghts.
> Are these the principal benefits and are these lenses that much better?

Theoretically, yes, but the term APO is bandied about by (mostly) off-brand
lens manufacturers as a semantic way of upgrading their products (ever
notice that Nikon and Canon avoid this designation [and their top lenses
are generally superior to the off-brand "APO" lenses...]?). Simultaneous
focus of three colors instead of two should result in better image
quality (especially for teles), but there are many fine lenses out there (including some teles) that are not apochromatic (and probably more than
a couple of "APO" lenses that aren't outstanding and/or apochromatic ;-).
I recommend selecting something for its actual quality, rather than its perceived quality (with an advertising- or mythology-enhanced product
image).
Hope This Helps