which ultrawide lens for me?

[photoferg]

Hi, I am moving up to xsi from p&s and I am driving myself nuts trying to decide which ultrawide lens to invest in.   I am leaning toward the tokina 11-16/2.8 because I do a LOT of night photography, and suspect my travel landscapes will be mostly hand-held or set on a hard surface with remote shutter release, but will that f/2.8 really be an advantage over, say, the sigma 10-20mm or the tokina 12-24mm or the canon 10-22mm?   And just to throw some more agitation into the mix, tamron(?) is set to release a 10-24mm lens that sounds great on paper - should I wait?   Are there some other lenses I should consider?   I rarely print photos, just play with them on the computer unless one is spectacular.   I don't plan to upgrade to a FF camera, in fact I haven't even received my xsi yet.  My other lenses are the xsi kit 18-55 IS, tamron EF mount 28-200 and tamron 200-500 (wildlife being my other favorite subject).  I can get a great deal on the sigma or the tokina 12-24mm if the wisdom here is that I don't need a lens as fast as the 2.8.    Also, I would like to get an extender for the long lens, should I look at 1.4x,2x or something else and which brand would you recommend?
Thank you in advance for any advice/recommendations, I think the resources in this forum are fantastic!
Nancy

[Bob Atkins]

If you're going to be doing a lot of night shots, you'd be well advised to get hold of a small tripod. Even a small "tabletop" tripod will be FAR more stable than handholding the camera and much more convenient and flexible than trying to find a flat surface.

I'd suggest looking at these:

Slick Tabletop Tripod - Conventional mini-tripid with ball head
Joby Gorillapod - Flexible leg tripod which can conform to many surfaces

When it comes to wideangle lenses, faster will allow shorter shutter speeds, but really for night work you want a stable suport so you can use a lower ISO and get better image quality. I'd personally value a wider zoom range and the ability to go down to 10mm over a lens that was a stop faster.

I have the Canon EF-S 10-22/3.5-4.5 USM myself and it's a very good lens. Well built, good zoom range, fast and silent focusing. If you can afford it, it's probably the lens of choice.

The Sigma 10-20/4.5-5.6 has a little less zoom range, is a little slower and is a little cheaper. I haven't used it myself, but user reports are generally favorable.

The new Tamron 10-24/3.5-4.5 hasn't been released yet. It can be pre-ordered from Adorama for $499 with delivery "expected soon". The zoom range is good and it's as fast as the Canon. The optical quality is as yet unknown, but based on results I've got from other Tamron lenses (including the 11-18), I suspect it will be pretty good.

So my choices would be #1 - the Canon EF-S 10-22, #2 the Tamron 10-24 (assuming it's available and performs as expected)  and #3 the Sigma 10-20

[photoferg]

HI Bob, I wanted to thank you for your excellent advice.   I decided on the used sigma 10-20mm (cost significantly less than canon) and have ordered the slik tabletop tripod  you recommended.   I'm looking forward to learning how to use all these new toys!  Again, I appreciate your help.
Nancy