There's lots of talk on the net about the 10-18 covering all of the full frame sensor of the A7r - with examples showing distortion and poor resolution at the corners. I went out to the garden yesterday and made an image, at 16 mm., no vignetting but definite blurring along the far sides. I did some checking and cropping and bottom line is if one trims the image to square, resolution is superb to the corners, this on a 24 inch square print.inspected from 8 inches away.
My intention to carry a large and heavy ultrawide is definitely on hold for now. Too bad the A7r can't be cropped in camera to square - now that's a firmware update I'd pay for, and maybe 4X5 ratio with this lens.
The widest view combined with a reasonable number of pixels is a 2:3 crop of 22 megapixels at 12 mm.
Given the small size and extremely light weight of the 10-18 - it will make an ideal travel lens for me this summer when I go to Newfoundland.
The Canon 70-200 L IS lens works great on magnified manual focus, and the IS is great - very sharp pictures at 1/60 and 200 mm. - perhaps that battery grip is helping shutter shake as much as some people say - anyway - works for me.
I have the 55 FE 1.8 native lens, and now just need something between a cropped 12 which is probably about 15 mm. equivalent, and the 55.
The sensible thing is probably the native 35 f2.8 since I don't need another fast lens, and perhaps a 24. I might lug the 24 Tse, but it's quite a weight on the A7r.
Anyway, in the mean time I will have no hesitation to use the 10-18 on serious landscape work.