Originally posted by sabzijoon I'll be traveling overseas and doing some sightseeing. So, my goal is to capture those moments. I usually do a lot of ultra-wide to wide angle photography especially because I like to capture the background. I also do landscapes, cityscapes and the like. I don't really know what's a good budget, but I can't afford too much. If there is something I can pick up under $250, then that'd be great.
OK - so 16mm wide end checks a box. What's the longest you need? If 45 does it I think you are close to sealing the deal.
Here are the contenders:
17-70 Sigma f/2.8-4 "Contemporary" - not as wide, faster, longer, not pentax color rendition, no in camera jpg corrections
17-50 Sigma f/2.8 - as above without the longer
17-50 Tamron f/2.8 - as above, not quite as well respected but supposedly very good.
16-45 Pentax f/4 - noisy focusing, out of production, some issues with decentering and lens barrel wobble I think.
17-70 Pentax f/4 - silent focus, sdm reliability issues, not quite as wide, longer reach.
12-24 Pentax f/4 - wide wide wide, very useable for street photography, out of budget
10-24 Tamron f/3.5-4.5 - wider than wide, still useful for street photography, not pentax color rendition
DA* 16-50 is out of the price range, and heavy.
HD DA 16-85 is a good lens but pricey compared to your budget I think.
I eliminated everything not at least 17mm on the wide end. This rules out the excellent 18-135 in my opinion.
Disclaimer - I have no personal first hand experience with ANY of these. I own an 18-135, and love it. It's my go to travel lens. I also own several nice prime lenses and some killer DA* zooms and some no so killer kit lenses. It's all relative. There are great pictures to be made with every choice you can make. Even dog lenses offer some options for creative use.
But based on what you said - travel, city use, wide wide wide angle desired etc. I think you have a good list here - go read some reviews next from the lens section to help you learn more. I don't think your first suggestion is a bad one at all but a lack of practical experience with it makes it hard to say.
---------- Post added 06-29-15 at 08:25 PM ----------
Originally posted by sabzijoon Will it be fine for taking shots at night? IT seems a little bit on the slow side.
At the wide end it is faster than the 16-45 you mentioned only on the long end is is slower. There is a chart one of the reviews on the site that shows how the f/stop changes with focal length. I am almost certain it isn't slower at 18-45mm than your original choice. The Sigma 17-70 is a little faster but mainly on the extreme short end.
Also remember that a single f stop separates f/5.6 from f/4 and likewise from f/4 to f/2.8 - that's not a lot on Digital with good high ISO performance. Use a tripod and enjoy. But in very dark situations you will want the extra light gathering or the wide open performance for subject isolation.