On my K-5 it works just fine. I can even stop down in a dimly lit room and use it without problem. I just ran a quick test and at ISO 800 on the K-5 and it did fine taking hand held shots at 1/50 even at f5.6 with no hunting... and the room I am in now is pretty dimly lit (with a single bulb lamp). It's just a trade off between ISO and aperture. It's not going to be some major issue with depth of field though. Wide open at 10mm 3 feet from the subject gives you over 6 feet of DOF according to my little calculator. 5 feet away is already at infinity. This kind of lens isn't for your bokeh shots. It all depends on what you plan to use it for. You can walk around outside and it gives some interesting options or you can use it indoors handheld... It's never posed a problem for me at all. Using an ultrawide is a bit of a different animal in my opinion. That goes for ANY ultrawide.
---------- Post added 09-04-13 at 08:35 PM ----------
Originally posted by wedge 
How is this lens for indoor/low-light use? I currently have the 28-75/F2.8 Tammy but find that sometimes it's just not wide enough. Was looking into the 17-50, but that doesn't seem to buy much more width and the large overlap in ranges makes it seem I wouldn't be gaining much. This range of FL seems more in tune with what I'd like, but, obviously, the aperture is smaller, so (in theory), it may not work as well in less-than-ideal lighting.
One of the things I have noticed in shooting Ultra wide is paying attention to lighting as a whole. It's actually "so wide" that unless you are paying attention half of your shot will be lit and the other half in shadows. That isn't a reflection of the lens but rather the focal length.
I own the 17-50 as well and that one is a great little lens too. I have been considering selling both merely because I have moved to an all prime line up for my shooting. For me I did a little thing called trial and error and tried to develop my own style of doing things and over time I just discovered I like primes. It's not much more complicated than that.
I also have the Tamron 70-200. I can tell you all about each one.... the 17-50 is sharper than most zooms and you won't be disappointed in that one. But like I was saying, when you go Ultrawide your field of view is just drastically different than what most people are used to.
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