Originally posted by sTi Doesn't anyone find it strange that the 20-40 contains no aspherical elements?
I admit I do find it a bit of a concern, but it does explain the size of the lens - aspherics help keep the size of lenses down, because the geometry of the elements themselves help keep spherical aberration, field curvature and coma in check, without them it is much harder to correct for things like that. Apsherics are much more common in shorter focal lengths than in longer ones - they are an unheard of rarity in 200mm lenses - yet they are quite common in lenses 50mm and under. Exotic lens elements made of Fluorite, HRLD, ED and SLD glass can be used as a substitute for aspheric* lenses however typically you need two or more of those types of glass to correct for the aberrations that could be eliminated by just one aspheric.
Originally posted by RobA_Oz just because they don't mention it doesn't mean there isn't an aspherical element. Still, you'd think they would mention it in the specification.
Pentax usually designate lenses with aspehics with "AL" E.G : DA15mm f/4. ED
AL Limited - though I prefer ASPH, as used by Leica.
Originally posted by NitroDC I don't understand how anyone can speculate on the quality of this lens when no one owns one yet and no sample images have been posted at all.
If Pentax had presented any images i'm sure there would still be a fair amount of speculation, we will have to wait for the lens to get in the hands of capable users to really see what its strengths are.
*but it is a less than Ideal solution with its own set of drawbacks and tradeoffs.