Tokina AF 10-17mm f/3.5-4.5 AT-X DX Fisheye - Review / Test Report - Analysis
Lens Reviews - Nikon / Nikkor (APS-C)

Distortion

The 10mm fisheye effect of the 10-17mm AT-X cannot be measured via the Imatest toolkit but the reference images below should give you an idea about the degree of barrel distortion (at 17mm: ~10%) - remember that the lens is supposed to do just that. This is not a design problem.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
10mm 17mm

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

Vignetting

Sorry - no vignetting figures this time. I'm absolutely clueless how to produce an evenly lit plane for a lens with a field-of-view of 180 degrees ... 8-)

MTF (resolution)

Testing a fisheye lens is a bit experimental. The Imatest toolkit freaked out regarding all the wild curves at the image borders at the 10mm setting. The 17mm MTFs should be quite accurate whereas the border resolution figures at 10mm should be only taken as a very rough guidance - the outer regions were not testable!

Keeping this in mind the Tokina Fisheye produced very good results in the lab. At 10mm the center performance is already very high at wide-open aperture and the borders follow not far behind. Stopping down produces only marginally sharper results. The local sweet spot is at f/8. At 17mm there's a very slight performance drop - not in the center but the borders suffer a bit at f/4.5. The situation is better at f/5.6 where the border quality recovers to very good levels.

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)

Lateral CAs (color shadows at harsh contrast transitions) can be quite a problem with the 10-17mm Fisheye. At 10mm the lens produces a quite excessive amount of border CAs (~2.5 pixels) whereas the situation isn't quite as bad at 17mm (~1.3 pixels). Please note that lateral CAs are correctable via imaging tools.

Purple Fringing

Lateral CAs may not be good but another aspect is purple fringing - a color blooming effect at extreme contrast transitions. Here's a 100% crop which should illustrate the potential degree of the problem.




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