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Tokina atx-m 11-18mm f/2.8 E - Review / Test Report - Analysis |
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Lens Reviews -
Sony Alpha/NEX (APS-C)
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Page 2 of 3
Distortion
Image auto-correction is the de-facto standard today. Activated, you don't have to worry about image distortions as you can see below.
When looking at the RAW characteristic, things change, of course, albeit not quite as much as on some other lenses that we have seen in this market segment. At 11mm, the lens produces a medium degree (2.4%) of barrel distortion. This eases the further you zoom out with neutral results at 14mm and marginal the barrel distortion is mild at 14mm and a marginal pincushion distortion at 18mm.
Vignetting
Auto-image correction also comes to the rescue when it comes to vignetting. While the light falloff isn't completely eliminated, it's not disturbing anymore at around 0.6 EV (f-stops).
The original vignetting characteristic is, of course, very different. As you might expect, the most extreme vignetting is present at 11mm @ f/2.8. A vignetting of 2.4 EV (f-stops) is beyond our usual scale for APS-C lenses. The vignetting is reasonably well controlled from f/5.6 onward at this focal length setting. Longer focal lengths are generally fine with a falloff of just over 1 EV wide-open and a bit less than that when stopping down.
MTF (resolution)
With their long expertise in designing ultra-wide zoom lenses, it isn't surprising that the Tokina atx-m 11-18mm f/2.8 E is sharp at most aperture settings. The center quality is excellent at all focal lengths from f/2.8 to f/8 and the near-center quality is just a tad behind. At 11mm the outer image field is good (albeit just) at f/2.8 and improves to very good sharpness at medium aperture settings. The wide-open performance is better at 14mm and the very high border/corner sharpness is maintained from f/4. The outer image field shows a substantial drop in quality at 18mm @ f/2.8 but improves rapidly at f/4 with impressive results from f/5.6.
Diffraction has a higher impact at f/11 although the results remain pretty usable. f/16 and beyond should be avoided - as usual.
The field curvature is marginal. The centering quality of the tested sample was Okay.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths
per picture height (LW/PH) can be taken to measure sharpness.
If you want to know more about the MTF50 figures, you may check out the corresponding
Imatest Explanations
Chromatic Aberrations (CAs)
Auto-corrected lateral CA (color shadows at the image borders) are nothing to worry about as shown below.
When looking behind the scenes, the original CAs are much higher albeit not on the extreme side. In the lower focal length range, they hover around a width of 1.5px at the image borders and a bit less so at 18mm.
Sun Stars (Experimental)
Below is s sequence of images from f/4 all the way up to f/16 - illustrating the Sunstar behavior (using LED lights). Sunstars are an aperture effect when shooting bright light sources such as street lights, the sun, etc. At f/2.8, thus at maximum aperture, the effect is very underdeveloped simply because the aperture is basically circular. The Sunstar effect increases the more you stop down - until a certain setting from where it diminishes again. If you scroll through the aperture range below, you may notice that the sweet spot is between f/5.6 and f/8. The light rays are "pointy", which is considered to be more desirable than the "fan" variant. You may also notice some lens flare effects, specifically at f/16.
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