Conclusion: Two questions, this test should give answers to, concern the cost-effectiveness of changing the kit lens 18-55 mm for Pentax 17-70 mm and a choice between the Pentax and the Sigma with the same focal length range. To tell you the truth non of these answers can be straight.
Cons: the manual focus ring moves too easy and is too small,, weak against the bright light performance,, too little frame corner resolution at 17 mm.
Pentax SMC DA 17-70mm f/4 AL [IF] SDM - Review / Test Report
16 December 2008
Conclusion: The Pentax DA SMC 17-70mm f/4 AL [IF] SDM is undoubtedly the most desirable standard zoom lens in the current Pentax lens lineup. The resolution characteristic is very good without any significant weakness. The vignetting and distortion are about average for a lens in this class.