Irix 11mm F4 Firefly & Blackstone

Distortions

Distortion refers to the capability of a lens to represent straight lines as...straight lines. Wide angle lenses often create barrel distortion, where lines look they've been put on a sphere. Telephoto lenses can create the reverse effect, named pincushion distortion. The following images illustrate the various types of distortion:

Barrel distortion, left; no distortion, center; pincushion distortion, rightBarrel distortion, left; no distortion, center; pincushion distortion, right

It is very difficult to create a zoom without some distortion. It is also very hard to design a wide lens, even a prime, which is distortion-free. On the other hand, normal and short tele lenses can more easily avoid the problem.

The way to evaluate distortion is pretty straightforward: take a picture of straight regular lines, and look if they curve. Calculating the ratio of curvature yields an evaluation of distortion.

Cameras such as the K-3 and K-1 include built-in distortion correction, which can be automatically applied to files captured files. These corrections are limited to the company's lenses, however. Irix lenses will not benefit from any correction.

Distortion Test results

The following images show how the distortion pattern looks when photographed with the Irix 11mm, for APS-C and full frame sensors.

APS-C

Full frame

As with the 15mm F2.4, the manufacturer provides distortion figures on its own website for the 11mm F4. Our findings are in accordance with these values, with 3.2% of distortion (Irix states 3.13%). This value is important, but to be expected for an extreme wide angle lens. Some lenses with a much more common focal length produce distortion almost as high. Relatively speaking, distortion is kept well under control.

One of the few other 11mm lens on the market, the Canon 11-24mm, actually suffers from much stronger distortion, reportedly reaching 4.5%. This latter lens is a zoom, of course, with lower expectations.

How does this translate in actual shooting scenarios? This first image illustrates what occurs when the lens is tilted a few degrees. The effect can become hard to miss, to say the least.

This second image demonstrates that, when used with care, distortion is not always bothersome.

Verdict

While the distortion value is high, at 3.2%, we cannot really blame the manufacturer. At this extreme focal length, some distortion is unavoidable. In-camera corrections would certainly help, were they available.


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