In general the lens seems to be very sharp, and the additional DOF is nice. (I used an online calculator to figure out focus settings for each usable aperture.) There's a little bit of barrel distortion, but it's only noticeable in certain pictures, and those can be adjusted.
The lens is low on constrast at f/3.5, and diffraction reduces sharpness a lot at f/16. So the only useful apertures are 5.6, 8, and 11, but that's fine for what I need. Focusing at the 2-meter mark at f/11 gives usable DOF from 3 feet to infinity, so I can't complain.
Any reactions to these pictures would be appreciated. I had some buyer's remorse that I didn't save up a bit more and buy a used Canon FD 17mm instead, but the distortion seems to be about the same, and the logical side of my head says this lens seems plenty sharp.
Update on this lens--while it generally seems sharp and well-built, I discovered tonight that the focus scale is very inaccurate.
I measured out 7, 8, 10, and 12 feet on the basement floor, since I planned to add a couple of focus marks (since the lens has a big gap between 2 meter and infinity). But when I focused on my test sheet, the lens scale read less than five feet when I was at seven feet; five feet when I was at 10 feet; and between 5 feet and 2 meters when I was at 12 feet.
I tried a Pentax 55mm, a Micro-Nikkor 55mm, and a Canon 100mm, and they were all really close.
Since I was planning to scale-focus the Tokina to maximize DOF, this could be a problem.
An update, fwiw--with a few aluminum-foil shims in the adapter, I've gotten the focus scale about as accurate as I can. Right now when the lens is focused at 2m, the focus mark is in the small space between 2m and 5 feet. That much difference I can deal with.
And, having looked over various sample photos, I think this is one of the best adapted lenses I've tried. Sharpness and contrast are very good. So I think I'll hold onto it as a slightly-wider backup for the 20/1.7, and just make a mental note to adjust slight when I need to scale-focus it.
Here's a test picture, scale-focused at f/11 in today's dull pre-snowstorm light:
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