Originally posted by redpigeons the 31mm have its name but its pricey and its not DA? ( maybe on cropped body I am not getting the best of this lens?)
on the other hand the 35 is cheaper and its DA but 2.8 is SLOW for a prime...
which bring me to my last questions why all the new Pentax primes for digital are slower then the FA ones? does digital sensor less demanding about speed?
(...)
As far as I know, it is not
proven that the lenses optimized for digital are that much different. "Designed for digital" lenses are supposed to prevent the reflections off the digital sensor, but that is not much of a deal.
Most lenses are not outresolved (meaning the lens is the limitation for 'sharpness', not the sensor) by the sensor, even with the K20D, and therefore the FA or DA designations mostly doesn't matter. The focal lengths are another story, as the lenses were generally designed for other uses (e.g. a 50mm, being the standard FL on film, becomes a lens well suited for e.g. portraits due to smaller field of view), film lenses may be somewhat "odd".
The DA35 isn't really that slow. Compare it with the 50/2.8 macros on film. See?
And the reason why the lenses are somewhat slow, is size and weight. The loss of a stop is being "justified" by the fact that digital sensors are better at higher ISOs than film was. In general, of course. Add shake reduction, and I bet a K20D with a DA Ltd. could win over a FA Ltd. on a film camera.