Originally posted by jjdgti I had several versions of the 28-200mm (Tamron) and also the 28-300mm. I also owned Tamron 18-250mm and Pentax DA 18-250mm lens. In my opinion, the 18-250mm is a far beter lens than the 18-200mm and the 28-200mm. If you can afford to buy the 18-250mm will be better. There are some used here in the marketplace for sale. Sometimes you buy a mediocre lens trying to save some $$ and get what you paid for.
The 18-250mm is a very good lens for trips. You do not need to change lenses during the whole trip and this is a Plus.
+1
The 18-250mm is a marked improvement from the older 18-200m lenses. However note that there are two generations of 18-250mm for Pentax K-mount:
(a) the Tamron/Pentax 18-250mm, and
(b) the Sigma 18-250mm OS HSM.
The Tamron/Pentax 18-250mm is highly recommended by many Pentaxians. As jjdgti pointed nicely, it is an excellent all-around lens allowing you to wokr with one body + 1 ens, avoiding len swappings. It is also one of the best all-rounders among all brands incl. Canikons.
The Sigma 18-250mm OS HSM is a newer, more expensive lens. The OS is not needed with Pentax cameras that have IS, and the initial users' reports are favorable.