are they not economically feasible? i know they EF-S line is more geared towards consumers who are more easily satisfied with superzooms and generally not interested in primes. basically what i want is a 28mm equivalent that's fast and sharp i.e. f/2.8 or a good 50mm equivalent that's fast i.e. f/1.8. i know about the EF 20mm 2.8 and the EF 30mm or 35mm i can't remember which, but EF-S lenses are typically cheaper. if i'm not mistaken Nikon just came out with a 35mm digital only lens. anyways, that's my question. so somebody who knows more about the economics or engineering of it, i'd love to hear your theories. thanks in advance!