Sigma 30mm F1.4 DC HSM "Art"

Distortion

The new Sigma 30mm exhibits a small amount of barrel distortion.  This means that near the extremes of the frame, straight lines will bend slightly inward.

Most of the time, this degree of distortion will not get in the way of your photography, but there are certain scenarios in which it might be easily-discernible in a real-world photo, such as when you have man-made objects near the edges or corners of a picture.

Current Pentax DSLRs only support in-camera lens corrections for genuine Pentax lenses, so to correct the distortion from this lens you must turn to a photo editing application with third-party lens profiles (such as Adobe Photoshop/Lightroom) or use manual lens correction tools.  The lack of in-camera corrections is a minor inconvenience.

To illustrate the degree of distortion, we performed the classic "brick wall test." Use the slider below to compare the out-of-camera image to an image corrected using Adobe's profile for this lens.  The nature of the distortion is simple, which makes it easy to correct even with a basic photo editor. We found the barrel distortion to correspond to a manual correction of approximately +2.3 in Photoshop.

Below is a sample photo in which the distortion manifests itself.  Notice how the lamp on the left side isn't quite straight.

Verdict

Our expectations of this lens were very high after seeing the impressive performance of Sigma's 35mm F1.4.  Overall, the Sigma 30mm F1.4 Art has slightly more geometric distortion than we'd like to see in a premium lens, especially one with a normal field of view.  The distortion is still within the norms for a prime lens, however, and due to its simple nature, it is easy to correct using desktop software.  We only regret not having in-camera distortion correct for this particular lens, as corrections are necessary at times to make images appear more natural.