The Canon EF-S 10-22mm is hard to beat. It's an excellent lens, well corrected, fast focusing, nice color renditions, super sharp, very good flare control (better than any other ultrawide I've seen). The only thing I'd tick as a negative is the lens hood is quite large... still, after testing I wouldn't be without it.
Tokina AT-X 12-24mm is the lens I rank second. It's also good in all respects, might even be better built (reminds me very much of a 17-35/2.8 L I had). It is not quite as sharp as the Canon and not quite as good handling flare. But still is excellent and better than most. It's also on sale right now (there's a new model out).
The Tokina 11-16mm is a popular lens for those who feel they need an ultrawide with f2.8 aperture. It's the only one that offers that. It is very sharp, close to or maybe even sharper than the Canon. However, it's quite prone to flare. Some people have no problem with that... Others have told me they ended up getting a different lens instead, because of the flare issues. I guess it depends upon what you shoot and how you shoot it, but flare can be an issue with lenses that cover a very wide angle of view. It's also a significant trade-off to get to f2.8, that this lens only has a very narrow range of focal lengths. All other ultrawides are at least 2X zooms. 11-16mm is only 1.45X.
Tokina has a new 12-28/4 out now, too... I have not used or compared it.
These three Tokinas and two Sigmas offer non-variable aperture design. All other ultrawides have variable apertures. This may or may not matter to you. I think the main place where variable aperture may be an issue is if using manual flash or studio strobes a lot. Variable aperture isn't a big deal for most.
Sigma offers a number of ultrawides. Their most affordable is a 10-20mm with a variable aperture. It's a decent lens that a lot of people find fine. I tried out an earlier version and decided I liked the Tokina better, so bought that instead (I now also have the Canon 10-22mm). Main thing I noticed was slightly less sharpness and more flare. But, do note that this lens has been revised once or twice since then and newer versions might improve upont this.
Sigma also offers a 10-20mm f3.5 with a non-variable aperture. It is quite large, heavy and more expensive. I have never used it.
SIgma also offers the widest of the wide... an 8-16mm. I haven't used it. It has strong, inherent wide angle distortion effects (almost as much as a fisheye lens). But that's to be expected with such an extreme lens.
There is a Sigma 12-24/4, too... but it's actually a full-frame capable lens (widest of the wide for FF, in fact), which makes it larger, more expensive and less well corrected. Not necessary for a 70D with it's APS-C crop sensor.
Finally, there is a Tamron 10-24mm. It's been many years since I tried one, but I seem to recall it was a bit soft in the 18-24mm range and didn't seem as well made as some of the others. It has been one of the more affordable and offered the widest range of focal lengths in a single zoom.
There aren't many prime lenses that are truly wide on a crop sensor camera. The only fairly affordable one that comes to mind is the Rokinon/Samyang 14mm f2.8. It's a manual focus, manual aperture lens that's full frame capable, but just barely gets into the ultrawide category for crop sensor cameras too. Sells under a bunch of different brand names, besides Rokinon or Samyang you'll also see it as a Vivitar (they call it a 13mm), Bower, ProOptic... maybe some more.
Most other ultrawide primes tend to be quite pricey (Canon's own 14/2.8L, Zeiss 15mm, for example).
You'll have to define what "best" means for you. All ultrawides have different pluses and minuses. You'll also have to decide what you consider "affordable". Have fun shopping!
What an excellent read you gave me sir! Many thanks indeed for the lowdown on the choices which exsist. Of course you know your stuff so I should really go into more detail as to what I am looking for, apart from a resonably priced wide angle lens.
Being a school teacher I am called upon to take group photos such end of year class photographs.
Having 30-40 kids together in a tight spot may give you an idea of what lens I should be looking at
I also take photos in small places such as rooms, park & play areas where I need to get as much in as I can into the shot.
Editing after means I can choose from my subjects without losing too much detail.
I am currently experimentng with my 50mm but as you well know, it falls short of what I need in shooting.
Although the standard 18-135mm lens is decent enough with the correct light condiitions I feel I would get much more creativity from a wide angle lens and fpr this reason I have to ask which would be your choice...the canon 10-22mm , which as you say is hard to beat... And next in line where a budget is concered, what would choose..?
The Tokina 12-24 mm..?
Many thanks, I look forward to reading more from you.
Apart from Flickr, are you anywhere else on the internet?
Given your stated requirements, you shouldn't expect a WA lens to be a panacea. Going too wide in a small room can easily generate unacceptable distortion.
True, but I also take outdoor shots most of the time and where the light is ver good. I am fortunate to live in an environment where daylight is usually very good. However, as you have written, which would you recommend from the previous answerer's selection of lens, given the knowledge of what I seek...
Many thanks in advance of your reply.
I'm not very knowledgeable about wide-angle lenses. I use the Tokina 11-16mm f/2.8 on my 7Ds and 50D. It's a good lens and very well made, but certainly not the sharpest lens I own. Now that I have a 5D3, I expect to eventually get Canon's new 16-35mm f/4. That lens, of course, wouldn't be particularly wide on an APS-C camera.
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