Originally posted by gemini 
about you it is fast?
all pentax 50-135 are similar fast or there are some lenses not fast (limons)?
pentax 50-135 faster then 16-50mm AF? or slower?
My experience is similar to the others, my 50-135 moves its focusing ring quite slowly. I was shooting indoor tennis the other day and the FA77, although not a fast AF lens by any means, was faster than my 50-135...
The 16-50 seems faster but it has its own quirks. It can hunt in low-light and sometimes at 16mm will confirm AF although it's clearly OOF in the VF.
Based on these experiences I have no great opinion about SDM. I feel the screwdrive is much faster. My D-FA 100, for example, has a long focus throw. But the speed in good light is very impressive. SDM is quieter, yes, but it seems slower and less reliable (lot of motor failures recently).
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