Based on raving reviews and numerous tech awards, I purchased the Tamron AF 18-250mm F/3.5-6.3 Di-II LD Aspherical (IF) Macro lens as my all-in-one zoom for my K10D (and now K20D) cameras last year. Personally, I think this lens blows.
When zoomed in on a subject more than say, 15 or 20 feet away, the contrast and clarity are severely lacking and fringing is absolutely horrible – making my images unsuitable for print – and
forget about cropping in tight. The lens seems to be in good working order, just really bad glass - or construction – or both. I mostly shoot urban and general nature photography. I tend to use a low ISO, mount the camera on a sturdy, pro tripod and ball head and I use a shutter release and the mirror lock function to minimize camera shake. I use Cokin filters, including polarizer, when/where necessary. And despite perfect exposure, I get the same dismal results (in regards to contrast and sharpness) at all apertures, in both manual and auto-focus, with and without noise and shake reduction, with and without filters, at low and medium ISOs, with and without the lens hood, and with both JPG and RAW image files. I clean my lenses, filters, etc., thoroughly, too. It’s just consistently lousy – even at fast shutter speeds (so the problem doesn’t seem to be from subject movement). I wanted an
‘everything’ zoom in the 18 to 200-300 mm range that would yield large prints with acceptable sharpness. The Tamron 18-250 is NOT it. The ONLY time I get acceptable results is if I’m within several feet of the subject, but that shooting distance seldom works for me. I didn’t realize I was getting a lens with so many caveats. E.g., must be within “X” amount of feet of subject for acceptable sharpness, or cannot print beyond 4x6” before low contrast, softness and fringing become painfully obvious, etc. On the other hand, images made on the same bodies with my Sigma 105 and Pentax 18-55 are awesome. Nevertheless, it’s bad enough that big, fast glass is not widely available for Pentaxians (especially as full DA/AF), but are we left with crummy telezoom options, too? Geez, I just want acceptably sharp photos from minor distances. Heck, I’d settle for
reasonably sharp at this point. Is either too much to ask of a telezoom? This is enough to make a P-shooter consider the availability, dependability and versatility of a Canon system. Sigh. Please tell me what am I missing, here.