Originally posted by GeneV Not my intent to bash Sigma as a brand at all. I own one that I like very much. I am just saying that the Sigma 18-250 is, to my knowledge, a relatively untested product in the Pentax mount. I don't hear much about it on this board, either. I would be far less inclined to send about $500 off for that lens than the DA 18-135, reviewed here. Now, if a test showed it to be equivalent or truly superior, that is another matter.
I have the Sigma 18-250 OS HSM. It is a bit better than I expected, but not as good as I had hoped. I have had some really good shots from it, and some that were disappointing. (I have to assume that the good ones were due to my abilities and the not-so-good ones are due to the lens' shortcomings.
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Seriously, the OS doesn't seem as good as the internal stabilization of the body, its focus speed on my K20 is fine, and the IQ is pretty good for a super zoom. That is all purely subjective, but that is my impression. (see my sig line).
The one thing that is not subjective is that, as with other Sigma lenses, it is not identified properly to the camera. The camera thinks it is a 70-200 so when using auto ISO it will let the shutter speed drop to 1/180 before raising ISO instead of holding at 1/250.
I agree with audiobomber. I will be surprised as well if the Pentax doesn't surpass it optically.