Tokina 11-16mm f/2.8 AT-X116 Pro DX
This is the Tokina version that uses the screw-drive for auto-focus. It has the same optics as the newer internal-focus motor “Pro II” version. The newer version also claims to have improved anti-reflection coatings. I have read that some users find the newer “Pro II” to be less sharp than this original version, but I suspect it’s just lens sample variation they’re seeing.
I’ll concentrate on the lens resolution performance in this article, in addition to my observations on any unusual behavior I have noted in using it.
Some people are averse to lenses that use the “screw drive” focus, but for me it’s basically a “don’t care” when the focal length is small (e.g. non-telephoto). Focus is still plenty fast (camera model dependent) and actually one of my more repeatable lenses for phase-detect focus.
An interesting thing I noted on focus is that the “live view” autofocus wasn’t consistent. This is the exact opposite of what typically happens with other lenses, where the “phase detect” is less consistent. I got such consistent results with phase detect that I used it for the resolution tests and got absolutely repeatable results. Since I only have one copy of this lens, I can’t say if you will see this effect or not.
Although it’s a “DX” lens, it has full frame coverage on FX at the 15mm-16mm lengths. I’ve read that corners are fairly soft on FX, but I haven’t tested it. Update 6-10-2016: I have tested it on a Nikon D610. It's very good at 16mm, but I don't like the level of vignetting at 15mm. See the my review here.
Tokina built this lens for professionals, so it’s a metal and glass hulk. It’s actually quite beastly in size and weight. It uses 77mm filters; I keep a UV filter on it, mainly because the front element is challenging to clean due to its substantial curvature. What you get for that big diameter: f/2.8 and constant-aperture while zooming!
What you don’t get: vibration reduction. Not such a big deal on short focal lengths, however.
These tests were done using a Nikon D7100 (24 MP) with unsharpened 14-bit compressed RAW format. I actually left the UV filter ON for the tests; the filter doesn’t have any measureable effect on resolution results.
I’ll let the pictures at the end of this article speak for themselves in regards to the anti-reflection coating and contrast. Yes, you’ll get internal reflections to show up when you point it at the sun; you will get flare when you “provoke it”, so don’t provoke it!
The lens also has a proper metal lens mount and gasket (rubber seal). That’s it as far as dust/weather resistance is concerned.
I read plenty of complaints about the focal length range only going from 11 to 16. I bought this lens for 11mm, so I really don’t care about how ‘long’ it can get; you’ll have to decide if this is important to you or not. You can bet that a longer focal length range would result in more optical problems. I am very pleased with the optical quality of this lens.
It would be nice if the corners were a bit sharper, of course. But when you compare it to the competition, you’ll see that the corner performance is actually first-rate. Note that in the resolution plots below you can get really good corner performance when you stop down.
Although this is a rectilinear lens, you’ll notice barrel distortion, particularly at 11mm. Since you can correct it using your favorite image editing software, it’s not a big deal. For landscapes, it is a total non-issue about 99% of the time. I bet you won’t even notice distortion when you get to 16mm.
What I didn’t notice was vignetting, which surprised me. Take a look at the sample photos at the bottom. Make it disappear with your image editor if it bugs you; same goes for any lateral chromatic aberrations.
This is a really great video lens. If you mess with focus while shooting video, you’ll want manual focus; it works by pulling the focus ring toward you to engage a clutch. I didn’t notice any focus breathing (grow/shrink image size with focus change), either. It also appears to be “parfocal”, so you don’t need to refocus after zooming.
Tokina 11-16mm f/2.8 with removable lens hood (plus 77mm UV filter).
This is why you should read this article. My goal is to enable you to evaluate resolution between lenses in a standard, scientific way. I also give you the information (see my MTF Cliff’s Notes article) to be able to repeat these tests for yourself.
Resolution measurements are in MTF50 lp/mm. This measurement represents how many image line pairs can fit inside a millimeter before the white-to-black chart transitions degrade to 50%; e.g. “turn to mush”. For me, anything beyond about 30 lp/mm is fine, and beyond 50 is outstanding. Higher-resolution sensors yield higher measurements, much like you’d expect.
Before I forget, you will notice a couple of tiny weird blobs in some of the resolution plots that follow. Please ignore these, since they are definitely not a lens imperfection. The measurement software is extremely sensitive, and an imperceptible chart surface indentation shows up very clearly in the measurements.
I use a (free!) program called MTF Mapper from here to measure lens resolution. The download site also has files for printing out the resolution targets (mine are A0 size on heavy glossy paper (‘satin’ finish seems to work just as well), dry-mounted onto a board). This program is covered in more detail in another article, but suffice it to say that this is really great stuff; it’s comparable to ‘Imatest’ in the quality of the MTF measurements, and it uses the “slanted edge” technology similar to ‘Imatest’, also. The author of MTF Mapper, Frans van den Bergh, really knows his stuff. Visit his site and give him the praise he deserves.
The chart design used for resolution tests orients all of the little black squares to be ‘slanted’ but they’re generally aligned in meridional and sagittal (think spokes on a wheel) directions to correlate better with the usual MTF plots you’re familiar with. There’s often a dramatic difference in sharpness between these two directions, and the chart photographs show it clearly.
The meridional/sagittal differences are what “astigmatism” is all about. This lens is decent in the sagittal direction when you get away from the lens optical center. Meridional direction isn’t nearly as good; this is the “norm” in most lenses.
The middle of the lens is beyond impressive, as you’ll see.
What the resolution target looks like. Mine is mounted ‘upside down’.
Finally, I’m getting around to some actual resolution results.
Tests were done with phase-detect back-button autofocus, IR remote, and a really big tripod. As I mentioned before, this lens likes phase-detect better than contrast-detect focus. I use the “best of 10 shots”; not every shot gets the identical resolution results. All cameras operate on the “close enough” principle for focus, so many tests are needed to determine the best resolution that the lens can produce.
MTF Mapper “focus target” plot. Note the “+15” fine-tune for phase detect.
Focus fine-tune was set to +15 to calibrate this lens to my D7100. Take a look at my MTF Mapper Cliff’s Notes article if you’re curious about the details. The lens is so wide that I had to have my A0 target at only 1 meter away.
Worst-case distortion at 11mm showing the resolution target
Same 11mm photo after software distortion correction
16mm uncorrected distortion. I don’t see any distortion.
The following measurements were done at the extreme focal lengths of the lens.
11mm wide open. Great center, corners not very good.
f/5.6 has outstanding center, and now corners are quite good.
Diffraction is killing resolution at f/16
16mm wide open. Again, corners aren’t that good yet.
f/4.0 has exceptional center, and corners are now fine
f/16 and diffraction is again killing resolution
f/22: Don’t go there.
Great for emphasizing the foreground. 11mm
Drinking Dragon (Los Arcos). 16mm.