Sigma 35mm F1.4 DG HSM "Art"

Sharpness

In order to gauge the Sigma 35mm F1.4's sharpness, we compared it to the Pentax 31mm F1.8 Limited using our star test chart.  This chart shows the limit of the resolving power of a lens.  The farther away from the center you see the blur, the worse the sharpness, and vice-versa.

Refer the the table below for the center sharpness results.  Click on any image to enlarge, and then scroll to compare the Pentax lens to the Sigma.  All images were taken from the same distance: roughly 4 meters.

Center Sharpness
Sigma		Pentax
F1.4		---
F1.8		F1.8
F2		F2
F2.8		F2.8
F4		F4
F5.6		F5.6
F8		F8
F11		F11
F16		F16
---		F22

The corner sharpness results are presented in the same manner below.

Corner Sharpness
Sigma		Pentax
F1.4		---
F1.8		F1.8
F2		F2
F2.8		F2.8
F4		F4
F5.6		F5.6
F8		F8
F11		F11
F16		F16
		F22

Actual photos (such as the full-size samples shown at the end of this review) may give you a better sense of just how sharp the Sigma 35mm is in real life.  The tests on this page do show, however, the the 35mm and the 31mm are neck-and-neck in terms of sharpness.  Considering the impressive performance of the tried-and-tested 31mm, this is great news for the Sigma.  Both lenses are very sharp in the corners of the APS-C frame, which is certainly not the case if the full image circle were to be examined on a full-frame DSLR.

Generally speaking, the Sigma 35mm is at its sharpest from F2.8 to F5.6, with F8 trailing not far behind.  Diffraction sets in at F11 and is pronounced at F16.  We are not surprised to see that Sigma decided to leave out F22 given the further degradation in image quality that we see going from F16 to F22 with the 31mm.

The bottom line in terms of sharpness is simple: both the Sigma 35mm F1.4 and 31mm F1.8 are incredibly sharp very wide-open, so don't hesitate to use these lenses at wide aperture settings!