----- Original Message ----- From: "Inner Focus" Subject: Re: Sigma HSM lenses for Pentax KAF mount
> Yes, interesting posts by the engineer who started that thread. The > conclusion is that ultrasonic motors CAN be faster, it's just that Pentax > have chosen a poor implementation (SDM) which doesn't make full use of the > technology, and thus it's results are far from optimal (they should have > chosen a ring-type motor instead of a micromotor). > "As far as I can ascertain, USM and SWM motors cannot be used in lenses with both in-lens and in-body drive systems, that's why Pentax uses the small ultrasonic motor similar to the competitions Micro-USM motors". Whether this is poor implementation from a couple of decades ago or not is the question. Unfortunately, twenty five years ago when auto focus technology was being developed, Pentax was floating rather aimlessly in the marketplace, and was giving the general impression of not having an R&D department. Anyway, what you were describing as a problem can be mostly fixed by turfing the cheap and slow lenses and buying better ones. I mostly use prime lenses, and really don't experience many problems with AF, with the major exception of when my dogs are running more or less straight at me. Pentax AF is pretty much on par with the AF from cameras in the same price league from the other manufacturers. William Robb -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
