... not 100% sure...
Main use will be motorsport - motorbike racing
Perceived Advantages:
HSM = fast focus speed?
Reach - my other zoom lens is Sigma 70-200 f2.8
sharp at f8
No other alternative (in zoom lenses) at this focal length range. A prime doesn't give me the flexibility I need (can't zoom with your feet at the track as only have limited points approved for photography)
Perceived Disadvantages
soft at 400
weight - 1.64 kg
IQ compared to 70-200 f2.8
I have considered the Bigma (no HSM, slow), 150-500 (1 stop slower and no better IQ), 100-300 f4 (no HSM in Pentax mount). I have a monopod if it gets too heavy to handhold. I have no problem handholding the 70-200 at 1.32 kg.
I have read reviews, user reports, and sought advice here. Reports are a bit conflicting but later examples appear to be better than when the lens was initially released.
Having problems getting a copy to test, and there are no local dealers that will hire it, and no dealers offer a return policy just because I don't like it. I have contacted CR Kennedy (local importer/distributor) to see if they can arrange a test copy but have had no response to date.
What advice can you offer.