There has been a lot of posts over the last few year about the use of APO in lens advertising. Apparently in advertising speak it does not necessarily mean apochromatic. However it does seem to universally mean, "It costs more". Sort of like the old term "Premium Beer".
Rob Studdert wrote:
On 16 Sep 2003 at 14:36, Alan Chan wrote:
I read somewhere that the Star in the Pentax lenses stands for APO, so it should apply to the apochromatic lenses. But I may be wrong...
I don't know the exact techanical differences, but Pentax & Nikkor use ED, while Sigma use APO.
The lens designation ED is not a definitive indication of lens performance it only indicates that the lens design utilizes glass with extraordinary dispersion characteristics.
The lens designation APO is an indication of measured optical behaviour. By definition an APO labelled lens will provide coincident focus on a plane perpendicular to the lens axis at at least three frequencies in the visible spectra. Unfortunately few "APO" labelled lenses actually achieve this and the lens designation APO is no guarantee that the lens may not have other significant optical aberrations.
As far as I am aware Pentax lenses with "*" designations mean nothing specific apart from being an indication that they offer premium performance for their class. So you could argue that like ED and APO, ASPH lens designations it usually purely a marketing tool and should be considered in context.
Cheers,
Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
-- graywolf http://graywolfphoto.com
