I think an important thing to understand is that the auto-ISO algorithims in Av mode is geared to protect against camera shake, not subject motion.
I shoot most of the time in Av mode, and the problem I've started having now I've got my DA21, is that in Av mode the shutter to allowed to drop too low to cope with subject motion. Previously I was shooting mainly normal to long focal lengths and the shutter speed was high enough to deal with subject movement.
One reason I'd like to upgrade to the K-5 is for the TAv mode so I can set the shutter fast enough even on wide lenses to cope with subject motion, whilst having control over the apperture.
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