Pentax-D FA 100mm F2.8 Macro WR

Distortion

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.

The 100mm macro WR is supposed to be a high-quality tele lens. Let's see how it fares regarding distortion.

Distortion Test

The way to evaluate distortion is pretty straightforward: take a picture of straight regular lines, and look if they curve. We at PentaxForums love brick walls, so this is what we will use.

A camera such as the 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.

The effect of distortion is all but impossible to see. Lightroom's correction profile for the lens recommends a value of 1 for the correction, which is the minimum possible.

Verdict

The 100mm macro WR creates a negligible amount of distortion, which will be almost impossible to notice in everyday shooting. It is truly a non-issue.