If you want to travel light with a lens only, the DA18-250mm is the best all-rounder lens. To be fair, the Pentax DA18-250mm is a Tamron rebadged lens, nearly identical to the Tamron 18-250mm. The image quality (IQ) and built quality of the Pentax and Tamron 18-250mm are basically identical: see threads at
www.Pentaxforums.com (search threads for 18-250mm). The DA18-250mm is regarded as one the leading lenses of its class.
An all-rounder lens like the DA18-250mm is ideal if you do not want to change the lens. It yields also a relatively small camera bag. For example, the DA18-250mm together with a Pentax body (K-x, K-20D, K-7) can fit nicely in a relatively small top-loader bag like the Lowepro Toploader TLZ1, together with the battery charger and a spare battery.
There are alternatives however. One consists in the the kit lenses 18-55mm WR and 55-200mm WR. The WR kit lenses are worth to consider if your camera is WR (eg K-7, K20D). Another alternative could be a few selected fast primes (eg FA20mm, FA43 mm or FA50 mm, DFA100 mm). Another option is a couple of zooms (eg 16-45mm & DA*50-135mm). There are other non-Pentax zooms that you may consider.
Personally, I travel often and I prefer to have a single lens always mounted on my Pentax. I genuinely like the wide range [18-250mm] offered by the DA18-250mm as well as it Image Quality.
Hope that the comment will help ... and Happy Easter
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