DA 12-24mm vs Sigma and Tamron 10-24mm Comparison
Image Quality: Distortion
The Pentax DA 12-24mm f/4, the Sigma DG 12-24 f/4.5-5.6, and the Tamron SP AF 10-24mm f/3.5-4.5 DI II lenses all have some degree of distortion. That is to be expected since most ultra-wide angle lenses are prone to distortion. The three lenses covered in this review are all rectilinear lens. They are designed to display images, such as horizontal or vertical lines in a straight pattern. The lenses should have little or no barrel or pincushion distortion. Barrel distortion would cause the lines to curve or bulge outward. Pincushion distortion would cause the lines to curve inward. Thankfully both types of distortion can be corrected by software, such as Lightroom or DxO Optics Pro
For this distortion test we found an evenly lit interesting brick wall that had regularly spaced joints. With the camera on a tripod, parallel and level with the brick wall, a series of shots were taken. We wanted to see how well the lenses were designed to eliminate distortion.
As you can see from the pictures above, if there is any distortion it usually occurs at the extreme end of the zoom range. In addition, we conducted a field test because although on the brick wall test it appears that the lenses have only a slight degree of distortion, on a larger scale the distortion can be very pronounced. On the side by side pictures below you will notice that the church appears parallel to the right side of the photograph.
The results of the brick wall and the field distortion tests clearly indicated that the Sigma DG 12-24 f/4.5-5.6 was by far the better lens of the three compared. The Pentax DA 12-24mm f/4 displayed slight barrel distortion at 12mm that cleared up by 15mm. The Tamron SP AF 10-24mm f/3.5-4.5 DI II had slightly more distortion at 10mm and 12mm than the Pentax, but like the Pentax cleared up at 15mm as well. There were no big surprises in the field test and all the lenses performed as expected. In terms of image distortion the Sigma came in first, while the Pentax and Tamron tied for second.