Originally posted by Athiril The 18-250mm is probably a terrible lens, im sure you can look it up online.
www.photozioe.de might have a test posted on it.
Any lens with such a huge zoom range will have obvious optical compromises.
The 18-55 kit lens isnt all that great, but probably trounces this.
edit: yep photozone got a test up -
Pentax SMC DA 18-250mm f/3.5-6.3 ED AL [IF] - Lab Test Report / Review
interesting to note, is that its a rebadged tamron 18-250
look at the 135mm results - absolutely dismal - only gets worse from there.
The fact that the K20D has a 14mp sensor will only compound this problem due to the (lack of) resolution of this lens and the small photosites.
Actually, the 18-250 is one of the best superzooms out there, per numerous tests and user reports. I can vouch for it personally on the K100D, K10D and K20D.
Perhaps the OP got a bad copy of it? I'd suggest returning it and getting another copy. The only compromises you'll notice from this lens is vignetting at the wide end, and a little edge softness at full zoom, which is to be expected. Some people have reported purple fringing, but out of thousands of shots with mine, I've only seen it a couple of times. Both the vignetting and purple fringing are easily correctible in post processing.
The 18-250 is a great walk around lens (easily equal to the 18-55 and 50-200 kit combo - I can't comment on the new 55-300 as I don't have it). You should get sharp shots with it (unless you're doing large upsizing, extreme crops, or viewing at 100% [not full screen, 100%]).
You can check the "Peru" set on my Flickr stream, or search the Pentax Photogallery for 18-250 shots to see what this lens is capable of. Here's one quick example with the Tamron 18-250 on the K20D:
Last edited by rfortson; 08-17-2008 at 10:42 AM.