There have been several threads on the 18-200mm and 18-250mm lenses for Pentax mount. See
PentaxForums.com - The Largest Pentax-Dedicated Photography Forum Community- Home and DPReview. In my opinion, there are 3 categories of 'single-lens' setup for the Pentax K-20, K-7 and K-x:
* the Sigma 18-200mm
* the Tamron 18-250mm and Pentax 18-250mm
* the Sigma 18-250mm OS HSM.
The first three lenses are older. The Sigma 18-200mm is the oldest. The Pentax 18-250mm is a re-badged Tamron 18-250mm. Both the Pentax 18-250mm and Tamron 18-250mm are regarded as far superior to the Sigma 18-200mm. See http:/http://www.photozone.de and
Camera lens tests, user reviews, camera accessory reviews - SLRgear.com! for example. The Pentax has an advantage over the Tamron: lens correction is available 'on-board' in the Pentax camera, but the Pentax lens is no longer distributed. All in all, see the excellent discussion on Pentax versus Tamron at
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/77388-18-250mm-pentax-tamron.html.
The newer Sigma 18-250mm OS HSM is said to be a nice lens, but it is quite pricy. Further the optical stabilisation (OS) of the lens is not really needed since the Pentax K-7 and K-x have already in-built image stabilisation (IS).
There was further recent interesting threads on the 18-250mm lenses for Pentax sDLR at PentaxForums.com
I have myself the Pentax 18-250mm with a K-7: it is a superb lens and I can recommend it very strongly. Like most 'single-lens', it has a few shortcomings (see the review in
Welcome to Photozone! for example), but there are some situations when one single lens is a great advantage: no need to change lens in tricky situations, light weight, small bag, ....
Last edited by hcc; 01-03-2010 at 01:56 AM.
Reason: Typos