Ultrawide | Prime or zoom?

[koolman]

Are any of the ultrawide primes better than others? I know Canon, Tokina and Sigma all have ultrawide primes. Any advice?

Right now I have a Tamron 10-24 which is fine but has a lot of CA and is far from tack sharp on the edges.

If you're considering a prime, I'd recommend picking a focal length first.  Your Tamron 10-24mm is equivalent to 16-38mm on FF.  Ultrawide is defined as <24mm (on FF).  If you want wider than your current 10mm on APS-C, that means a 14mm prime (Canon, Samyang) or the Sigma 12-24mm zoom.  There is the 17mm TS-E, 20mm primes from Canon and Sigma, and zooms from Canon (17-40, 16-35) and Tokina (16-28).

Of those, the best optical quality will be the 17mm TS-E.

neuroanatomist: For a crop - t2i - would you recommend as a "walk around lens" with IQ in mind not budget, the 16-35 ?

[Axilrod]

Are any of the ultrawide primes better than others? I know Canon, Tokina and Sigma all have ultrawide primes. Any advice?

Right now I have a Tamron 10-24 which is fine but has a lot of CA and is far from tack sharp on the edges.

If you're considering a prime, I'd recommend picking a focal length first.  Your Tamron 10-24mm is equivalent to 16-38mm on FF.  Ultrawide is defined as <24mm (on FF).  If you want wider than your current 10mm on APS-C, that means a 14mm prime (Canon, Samyang) or the Sigma 12-24mm zoom.  There is the 17mm TS-E, 20mm primes from Canon and Sigma, and zooms from Canon (17-40, 16-35) and Tokina (16-28).

Of those, the best optical quality will be the 17mm TS-E.

neuroanatomist: For a crop - t2i - would you recommend as a "walk around lens" with IQ in mind not budget, the 16-35 ?

I have the 16-35mm II and the 14mm f/2.8 II and while I love the versatility of the 16-35mm, the 14mm is crushing it in terms of sharpness and color.  14mm is very very wide on Full Frame, but if you want ultra wide you wouldn't be disappointed.  At the same time it's significantly more expensive than the 16-35mm. 

I would 2nd the vote for the Zeiss 21mm, I was pretty blown away with it's sharpness across the entire frame.  I am most likely selling my 16-35mm for a that or a 24L II. 

[neuroanatomist]

neuroanatomist: For a crop - t2i - would you recommend as a "walk around lens" with IQ in mind not budget, the 16-35 ?

Actually, I'd recommend the EF-S 17-55mm f/2.8 IS as the best general purpose zoom for an APS-C body.  On the same APS-C body, the IQ of the 17-55mm is better than the 17-40L, slightly better than the 16-35L II, plus the 17-55mm has a broader range and IS.  With a 7D, the weather-sealing of the 16-35L might be a factor, but not with a T2i.

[Axilrod]

neuroanatomist: For a crop - t2i - would you recommend as a "walk around lens" with IQ in mind not budget, the 16-35 ?

Actually, I'd recommend the EF-S 17-55mm f/2.8 IS as the best general purpose zoom for an APS-C body.  On the same APS-C body, the IQ of the 17-55mm is better than the 17-40L, slightly better than the 16-35L II, plus the 17-55mm has a broader range and IS.  With a 7D, the weather-sealing of the 16-35L might be a factor, but not with a T2i.

I'd 2nd that, IMO it's sharper than the 24-70, I was really surprised the first time I played with it.  Also it's an effective   However I remember having my T2i and being pretty damn impressed with the 16-35mm on APS-C, the bokeh is very circular and looks beautiful cropped. 

But in terms of versatility, Neuro is right, the 17-55 is awesome.  The only bad thing I've ever heard about the lens is that its somewhat susceptible to dust.