Hmm, why not the Tokina 10-17 then?
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opticallimits.com
Also consider any 8mm fisheye, they are dirt cheap, yet quality is excellent DOF is so big focusing is never an issue, I don't think manual aperture is a problem, you set the focus on the estimated distance by reading on the lens barrel set aperture and shoot, you will use viewfinder only for composing not focusing
Hm, well, on APS-H you might have to look for a Tokina without hood already.
The EF 15 is not wide enough?
One fact in favour of the Tokina (and also the EF 15) is size: the 8-15 is quite bulky in comparison.
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opticallimits.com