I bought the Sigma 10-20 F 3.5 before going on a cruise. Unfortunately I didn't have a chance to test it before the trip. Attached are two examples where there is extreme distortion. Shots taken without a person seem fine. Shots taken where the person was in the center of the frame seem fine. Both shots were taken at 17mm. I have a 16-85 Nikon, and have never had any issues at 16.

Bottom line, do you think I have a defective lens, or is this what I have to expect from an extreme wide angle?

Probably a stupid question, but is there any way to fix this post processing?

I am about to head to Banff, and it really makes me think twice about using this lens with people and scenery.

Thanks for any advice.