How important is a fast aperture in a wide angle lens?

I am looking for a good wide angle lens: I am looking at the Sigma 8-16.

It has great reviews, by far the widest angle I can get on my camera. Only thing I am worried about is the relatively low f4.5. I do a lot of shooting in bars and nightclubs, one of the reasons I want a wide angle lense is to be able to take group pictures more easily. Right now my widest lens is the 18-55mm kit lens, but I mainly use the 35mm 1.8. So this would be SIGNIFICANTLY wider, but not nearly as nice of an f-stop. That being said I always shoot with my SB-600 anyways, so I don't think it would be that big of a deal.

The other option I am looking at is the new Tokina 11-16 Ver II.

Nice fast f2.8, but more expensive and not as wide (though 11 is still a lot wider then I have been working with).

Do you think have a f4.5 will be too much of an issue when shooting in indoors/relatively low light when i am using a nice flash (and my camera handles high ISO fairly well, plus I am pretty good with Lightroom noise reduction)?

Answer

First off 11mm is very wide, well into the so wide it's difficult to use territory. I can't imagine anyone feeling stuck with 11mm not being wide enough. You are likely however to run into problems with people looking stretched at the edges of your images, or getting too much unnecessary foreground detail in shot. Secondly you'll be able to use slower shutter speeds than you could with the 35mm lens so the aperture is less of an issue.

You should be aware though that ultra wide lenses are often not very Sharp wide open, particularly at the borders.

If you want wide and fast then you're a bit stuck on a crop body. I first upgraded to full frame for this very reason. I needed more options to shoot events in poor light where flash is not practical. On a full frame body you can get a 24mm f/1.4 lens. The fast lens matching that on a crop would be 16mm f/2.8, which is two stops slower. Two stops is a big deal.

I really don't think you need to go any wider than 24mm equiv. due to the problems mentioned above. Cutting through the crowds and making space for yourself are very useful skills. If I were you I'd stick with the 17 kit and save up for a full frame camera, used bodies are becoming available at good prices now.