Sigma HSM?

[chrism_scotland]

Hi folks, looking for a little advice, I'm looking for a walkaround for my Pentax K20D and seem to have settled on a Sigma 17-70 as the best value option without spending a fortune, now I've sourced a couple of possible used options on the older non HSM version (and non OS)

I wasn't bothered about getting the lens without OS as like Sony and Olympus I have in body IS, however I was wondering what difference having the HSM motor makes v the older version without?

Apologies if this is an obvious question but I never had the option of HSM on any previous Sigma Sony mount lenses I owned.

 

[squishy]

Faster silent focussing.

Being pentax, in non HSM it'll probably use the screw drive.

 

[mjjiva]

very good value for money, I'm still in the process of sourcing a pentax k-5 and a 31mm 1.8. but for a general walk around I'll be considering the sigma 17-50mm hsm , which has had quite a few favorable reviews but is twice the price of the 17-70mm