APO & Non-APO difference

[3 Olives]

I am not in the market for either. However, I'm curious to read whether it makes a big difference in the quality of an enlarging lenses.
If so, which APO lens for the home developer makes the biggest difference?

 

[fschifano]

The APO designation on a lens simply means that the lens will focus three colors on the same plane. The more common achromats are optimized to bring only wavelengths into focus on the same plane. Apochromatic lenses are also corrected for spherical aberrations for two wavelengths of light, where achromats can be highly corrected for spherical abberations at only one. Does this really matter? Well, not really in many circumstances. If you are making very big enlargements, say greater than 10x or so, or your work requires a very high degree of accuracy for color separation work, then yes, an APO lens is an advantage. For general B&W work when enlargments are often no greater than 10x, you'll not see a difference; but you will pay a much higher price for an APO lens over the more common achromats.

 

[Eric Rose]

For color printing they do make a difference but for B&W there is no observable difference. I did exhaustive testing between apo and non-apo lenses some years ago and those were my findings.