DA* 16-50mm vs. Sigma and Tamron 17-50mm F2.8 Comparison

Image Quality: Distortion

For this test, we placed the test camera on a tripod pointed at a brick wall. We shot each lens at 16 or 17mm, 35mm, and 50mm. (Alignment may not be perfect, but this should give you a decent idea of the lenses' distortion characteristics. Apologies for the shadow in the 16mm Pentax image.)

• Single-point Live View autofocus (on center of scene)
• ISO 100
• Aperture: f/8
• JPEG (highest quality)
• White balance set to Auto
• Auto-exposure; Multi-segment / Evaluative metering
• Image mode set to camera default ("Bright")
• Dynamic range extension off; In-camera lens corrections off
• Camera on tripod, 2-second self-timer; SR off (OS off for the Sigma)

Conclusions

All three lenses display significant barrel distortion that verges on moustache (aka "wavy") distortion at their widest focal lengths, with a characteristic "bulge" in the center of the image creating barrel distortion only at the centermost area of each side of the image. The effect is most pronounced on the Pentax, probably due to its slightly wider field of view. All lenses are effectively distortion-free at 35mm and 50mm—though there may be a slight degree of pincushion distortion, it's not exactly field-relevant.