Northern lights? Then go for the 11-16, it's a no brainer. The extra stop or two will make a fair difference. You don't really need to worry about the DoF in shots like that as the foreground will still be in focus even a few feet away when focused at infinity.
DoF calculator suggests at 16mm and f/2.8 you will get everything in focus from 8ft to infinity... (Just for clarity).
The only negative for the 11-16 is the zoom range. It's almost disingenuous to call it a zoom, but that's the trade off you make for the fast glass.
Sigma 18-35mm F1.8 is worth considering too although it's not 'that' wide on paper but I find 18mm is often plenty I prefer my 18-35mm to my 10-22mm EF-S lens
F1.8 would be a bit faster again for the glowy stuff in the sky
Thanks for the info guys, the Tonika seems great, though I realise photography is expensive I am after something a bit cheaper than £400 so I'll look out for some mint second hand lenses. Got an expensive Holiday coming up soon!
Haven't tried the Sigma personally, but was put off by the reviews; Seems to be a wide variation in quality from good to absolute parp.
-Leezer
Just looking at some 18mm Northern Lights shots and they look great, definitely something I'd be satisfied with. My current lens is a Canon EF-S 18-55mm f3.6-5.6 IS STM Lens though... so I'd still need something with a lower aperture (2.8) though?
Or go full frame and get the soon to be announced Canon 11-24 F4L