Tokina AF 16-28mm f/2.8 AT-X Pro SD FX (EOS) - Full Format Review / Lab Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)
Article Index
Introduction
Analysis

Distortion

Ultra wide angle lenses usually show a considerable amount of barrel distortion but the Tokina has comparatively few problems here. There is, of course, some moderate to heavy barrel distortion at 16mm but we've seen a lot worse. The issue has eased significantly at 20mm already (1.4%) and there isn't really anything to complain anymore at 24mm (0.6%) and 28mm (0.1%). The characteristic is slightly wavy at the longer focal lengths though so the remaining traces are not that easy to correct (if necessary anyway).

Move the mouse cursor over the focal length text marks below to observe the respective distortion
16mm 20mm 24mm 28mm

The chart above has a real-world size of about 120x80cm.

Vignetting

The Tokina lens shows only a very moderate light falloff especially considering its focal length and aperture class. There's naturally some vignetting at 16mm @ f/2.8 but at around 1.6EV it's a full stop better than e.g. the Canon EF 16-35mm f/2.8 USM L here. The falloff is slightly better at the other focal lengths at max. aperture and not really a problem anymore when stopping down to f/5.6 at 16mm and f/4 at the other focal lengths. This is quite an achievement for such a lens.

MTF (resolution)

The Tokina lens has a mixed resolution characteristic but considering its common real world aperture use it's highly impressive nonetheless. The weakness of the lens is the corner performance at max. aperture. The center quality is already very high and the borders are also good to very good but the corners are generally soft here. The corners receive quite a boost at f/4 but they become very good from f/5.6 onwards. The center performance is superb straight from f/2.8 at 16mm and 20mm and very good at f/4. Stopping down to f/4 to f/8 results in an excellent center quality throughout the focal length range. The border quality is generally very good in the lower range at all settings with a very good to excellent peak around f/5.6. The sweet spot of the lens is around 20mm. Field curvature is not a big issue.

This may sound quite enthusiastic actually but we've to note that we've purchased three samples for testing - two for Nikon and one for Canon EF mount. All three showed fairly significant centering issues towards the 28mm setting. The initially delivered Nikon variant was below testing quality and we had to return all three actually. A "golden sample" will perform better at the longer focal lengths. However, there's a limit to how many samples we're willing to test here to get one.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Chromatic aberrations (color shadows at harsh contrast transitions) are moderate at ~1.6px on the average at the image borders at f/2.8 and around 1px at medium aperture settings . This is, again, pretty good for an ultra wide-angle lens although the problem may be visible at times. It is, of course, possible to correct lateral CAs in most modern RAW converters.

Verdict

The Tokina AF 16-28mm f/2.8 AT-X Pro SD FX is a high-performance ultra-wide zoom lens that gives the Canon EF 16-35mm f/2.8 USM L II a run for the money - but it's not a lens without flaws. Its primary weakness is corner softness at f/2.8 but that's not unheard of in this class anyway. However, the center quality is great and the borders are generally sharp as well. The corners start to catch up at f/4 and they're very good from f/5.6 onward. Vignetting is, of course, visible at f/2.8, specifically at 16mm but the issue is better controlled than average. Lateral CAs, an old Tokina disease actually, are modest and not overly field-relevant when stopped down a little bit. Typical for such lens it shows some barrel distortions but they're, again, comparatively moderate even at the very wide end of the range. Technically the Tokina is superior to the current Canon EF zoom lenses in basically all the analysed image aspects!

Unfortunately there may be a hair spoiling the (optical) soup here - quality control. As mentioned we purchased three lens samples for testing, two in Nikon and one in Canon mount, and all three showed some centering issues. The initial Nikon variant was so poor that we had to cancel the testing procedure. We'd like to urge the manufacturers to take lens centering (alignment) more seriously - just a good or possibly even great base-design is simply not enough without proper manufacturing. We are pretty sure that consumers, especially in the mid-to-high end market, would be happily willing to pay a little more for better quality control. Especially ultra-wide and standard lenses show more outliers than desirable - not only among Tokinas but across the manufacturers (e.g. recently we tested 3 (three!) Sigma 8-16mm f/4.5-5.6 in Nikon mount without success). We are probably seeing negative outliers in excess of 25%(!) in this segment which is, frankly, embarrassing and unacceptable!

That all said we'd like to end this review with some more positive aspects. The (outer) build quality of the Tokina is on a very high level. The lens body is only based on tightly assembled, high quality plastics rather than the "duraluminium" finish used in previous AT-X lenses. However, the quality is still up to pro standards with the exception of the missing weather sealing. Tokina has improved the AF quite a bit - it doesn't really operate "silently" as promised but it's both fast and accurate in phase-detection AF mode. Some users may not like the huge, bulb-like front element which prohibits the use of front filters. However, it seems as if only this design approach solves the performance issues that are usually associated with ultra-wide angle lenses. So setting aside potential sample variations the Tokina is definitely worth a deeper look!

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