Tokina ATX-M 11-18 mm f/2.8 E
6. Distortion and field of view
Distortion
Nowadays there is a trend for neglecting distortion in lenses and leaving its correction to the camera's software, especially when it comes to wide angle lenses. Perhaps it is a good solution but it has a drawback in a shape of truncated images and resolution losses.That's why you should praise these few producers that still try to correct distortion with optics like the tested Tokina. What's more, that correction is quite successful in the majority of cases.
Distortion is noticeable at the shortest focal length, as it reaches −2.82%. Still, any results with absolute value lower than 3% we consider to be not especially bothersome and the Tokina fits that range.
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At the longer focal lenths the situation is even better. At 13 mm distortion decreases to −1.05%, and at 15 mm it becomes almost zero, with an official result of +0.08%. By the maximum focal length you already deal with pincushion deformations of a very slight level – just +0.85%.
It's also worth mentioning that the lens doesn't forces distortion correction by the camera; if you leave this option switched off in the menu the aberration won't be corrected and will remain the same for RAW and JPEG files.
| Sony A6400, JPEG, 11 mm | |||
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| Sony A6400, JPEG, 13 mm | |||
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| Sony A6400, JPEG, 15 mm | |||
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| Sony A6400, JPEG, 18 mm | |||
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Field of view
When it comes to an ultra wide angle lens every degree of the field counts so we decided to check whether the official specifications of the producer are true. In order to do that we took photos of starry sky for both ends of the focal spectrum using uncorrected JPEG files. In both cases we used about 70 stars, positioned more or less evenly across the whole frame, to transform the grid of coordinates. The relative mesh-fitting error amounts to 40 seconds of arc for the 11 mm focal length and 17 seconds of arc for 18 mm.Our measurement of the field of view at 11 mm provided a result of 103.91 deg so a value, within the margin of error, in complete accordance with 104 deg, stated by the producer. In the case of 18 mm the situation was the same – we got 76.8 deg and the field in official specifications is 77 deg. With such small differences we can say the Tokina provides exactly what it should when it comes to angles of view.
