HD Pentax-DA 35mm F2.8 Limited Macro

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, 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, that is distortion-free. On the other hand, normal and short tele lenses can more easily avoid the problem.

35mm lenses can show varying levels of distortion, depending on their design. However, macro lenses are usually expected to control distortion better than regular lenses. Is it the case with our test subject?

Distortion Test

The way to evaluate distortion is pretty straightforward: take a picture of straight regular lines, and look if they curve. Brick walls work well for this purpose.

A camera such as the Pentax K-3 includes built-in distortion correction. In order to measure the actual performances of the lens, we shot our test picture in RAW+, and compared the uncorrected, RAW output with the corrected JPEG result. The slider below illustrates both results.

Distorsion is subtly visible when comparing the images, but is negligible for most realistic shooting situations, measuring at 0.4%.

Verdict

The DA 35mm creates a very small amount of distortion, which will be almost impossible to notice in everyday shooting. In addition, the built-in correction profiles in recent cameras, and the lens profiles included in programs such as Lightroom, seamlessly remove what little effect there might be.

This is very commendable, since wide lenses often show stronger distorsion values than longer lenses. An excellent result which will be useful in particular for macro work.