The Pentax 18-270mm performs well overall for a superzoom lens, and it has filled an important gap in the Pentax lens lineup.
The 18-270mm is meant for casual Pentax DSLR users who want to stick to just one lens. Because it is compact and covers such a broad zoom range, it's the ideal travel lens. Its silent autofocus is a very welcome addition compared to its predecessor, and it's good for shooting in bright daylight because of its excellent flare and aberration control. Its smooth bokeh also makes it a good choice for portraits and family photos. Get this lens if you need the extra reach that the kit lens does not deliver, or if you want a super-zoom with silent autofocus.
With an effective zoom of 15x, the 18-270mm offers the most convenient focal length range of any lens currently in the Pentax lens lineup. This lens isn't stellar optically or in terms of AF speed, but overall, it actually did exceed our expectations somewhat. The fact that this lens is made by Tamron only shows itself because of the lack of quick shift focusing (meaning that you have to flip the AF/MF switch to focus manually); in all other aspects, this lens has been flawlessly adapted for Pentax.
If you plan on making larger prints or are concerned with speed or image quality, then this lens isn't for you. We may even go as far as saying that if you plan on owning multiple lenses, then this shouldn't be one of them. For enthusiasts who wish to complement their lens lineup with an all-in-one lens, we recommend the Pentax 18-135mm WR instead, as it's cheaper and offers weather sealing as well as slightly better image quality at the focal lengths that it covers.
However, even though this lens has some quite pronounced distortion/vignetting and is soft near the edges, it is certainly still capable of capturing great images. When paired with a modern DSLR, such as the Pentax K-5 or K-30, and powerful photo editing software such as Adobe Lightroom, you'll be able to push this lens to its limits and you could end up with images that are quite good technically. Overall, we were quite pleased with the results we got with this lens at the K-5 while shooting landscapes (see the sample photos on the previous page), and thus we aren't hesitant to recommend it for beginners. Our photos saw minimal processing beyond one-click lens corrections and level adjustments. This lens is not recommended for a mirrorless cameras (the K-01) or live-view shooting because contrast detect autofocus is neither fast nor accurate with this lens, most likely due to the small maximum aperture at longer focal lengths (F5.6 - F6.3).
The one big downside to this lens is its high price. The original launch price of $799 is $250 more than the Sigma 18-250mm Macro HSM, which was launched at the same time as the Pentax 18-270mm. Considering the fact that the Pentax 18-135mm can be had for $300-$450 and that most Pentax DSLRs are actually cheaper than $799, the way this lens is priced simply doesn't make much sense.
This lens shines in some areas but is lacking in others, and thus all-in-all we give it only an average rating. It did not impress us much in terms of its image quality, but this shortcoming is made up for by the convenient zoom range and small form factor. Weather sealing would have made this lens a much better value given its high price.