Excerpt: The star attraction on the Tamron 18-250mm f/3.5-6.3 Di ll LD (IF) Macro is the impressive focal range. The massive 18-250mm range makes this the world's only 13.9x zoom lens (based on Tamron's research into lenses for DSLRs) designed for DSLRs with APS-C sized sensors. Once mounted on your camera, the 18-250mm will give you an effective focal length of 27-375mm (1.5x) or 29-400mm (1.6x), which is pretty impressive in anyone's book.
Tamron AF 18-250mm f/3.5-6.3 Di II LD Aspherical [IF] macro (Nikon) - Review / Lab Test Report
30 September 2007
Conclusion: Early user comments already suggested that new Tamron AF 18-250mm f/3.5-6.3 Di II LD Aspherical [IF] macro does not only offer a longer range but also a higher quality over the old Tamron AF 18-200mm XR and the lab results confirm these impressions. The results may not touch the sky but the new AF 18-250mm delivers a very solid performance for most of the range. Unsurprisingly the weak spot is at 250mm @ f/6.3 - stopping down to f/8 is a good idea here.