What is an anastigmatic refractor objective?

I've seen this in several manufacturer "ads" now as something special. I understand it pertains to the lack of particular optical aberrations i.e. perfect lens. Without digging into "Telescope Optics..." I'm curious if the highest quality apos like AP/TEC etc as well as maybe the D&G achromats...all of which are painstakingly figured and corrected to eliminate secondary aberrations ('cept for focal length related CA in the latter) can also be considered "anastigmatic"? My gut tells me this may be just marketing mumbo-jumbo to separate themselves from the pack and impress the impressible, or is this actually a valid optical attribute only the luckiest and most fortunate telescope users should pursue?

Thanks, Pat

An anastigmat is corrected for spherical aberration, coma, and astigmatism. It may have varying levels of correction for chromatic aberration and/or spherochromatism.

Pat...any modern photographic lens is anastigmatic...it isn't anything *special*...and most well made achromatic telescope objectives are anastigmatic. Generally, Chromatic effect is an issue of focal length and the index of the elements used in the lens design.....you do know that achromatic means *color free* and we hardly consider most achromats *color free*...when the apochromatic now seams to fit that bill. Anastigmatic is as ED used to be...it is a selling tool.

Patrick Kelly said:

I've seen this in several manufacturer "ads" now as something special. I understand it pertains to the lack of particular optical aberrations i.e. perfect lens. Without digging into "Telescope Optics..." I'm curious if the highest quality apos like AP/TEC etc as well as maybe the D&G achromats...all of which are painstakingly figured and corrected to eliminate secondary aberrations ('cept for focal length related CA in the latter) can also be considered "anastigmatic"? My gut tells me this may be just marketing mumbo-jumbo to separate themselves from the pack and impress the impressible, or is this actually a valid optical attribute only the luckiest and most fortunate telescope users should pursue?

Thanks, Pat