« on: February 06, 2012, 05:28:24 PM »
I have the 17-40, but I've never used the 16-35 (either version) for comparison. At f/16, it is pretty soft in the corners at 17mm on full frame, but it is handy for specific effects, particularly where you can use the distortion creatively. Once you get to 24mm though, I find it is sharper than my 24-105 and there is certainly less barrel distortion. As with any UWA, use of polarisers is problematic, if you point it towards the sky and you can't really use it fully zoomed out with a second section of a Lee filter set, as the adaptor is in frame in the corners.
to solve this issue buy a cheap ebay cokin filter holder (the plastic one) only a couple of bucks
and get a hack saw then saw off the extended holder section so you only have 1 filter slot. I find doing this stops the corner interference on full frame at 16mm. it introduces another problem in that light gets in between the filter and the lens so you need to make a little shroud that goes around the edge of the square filter and over the lens barrel. hope this helps