Sigma 30mm F1.4 DC HSM "Art"

Sharpness

Once focused correctly, the Sigma 30mm F1.4 "Art" is incredibly sharp.  The example photo below was taken hand-held with a Pentax K-3 and the lens set to F4.  The superb detail visible at 100% is a testament to the sharpness of the lens.

Sigma 30mm Sharpness

But before we proceed, we need to take a look at the sharpness at other aperture settings, as well as the corner sharpness.  We will be comparing the Sigma 30mm to the Pentax 31mm Limited, which is known for its sharpness and thus will be used as our baseline.

When looking at the star charts that follow, the closer the lines get to the center of the image, the better.  Conversely, the more "fuzz" you see around the center, the worse the sharpness.  The star charts were photographed in our studio at a distance of 3 meters for the 30mm and 3.1 meters for the 31mm.  All images below are unscaled 100% crops from the Pentax K-3.

Chart Test 1 - Center Sharpness

Sigma 30mm
Pentax 31mm

F1.4

F1.8

http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6674.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6682.JPG
F2 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6675.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6683.JPG
F2.8 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6676.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6684.JPG
F4 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6677.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6685.JPG
F5.6 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6678.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6686.JPG
F8 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6679.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6687.JPG
F11 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6680.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6688.JPG
F16 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6681.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6689.JPG
F22 --- http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6690.JPG

Our first test shows that the 30mm is incredibly sharp from F2.8 through F8 and quite good wide-open and at F2.  Diffraction starts setting in at F11 and significantly degrades sharpness at F16.  Sharpness improves as you stop down, peaking at F5.6 and only worsening slightly at F8.  The only major issue at F1.4 is low contrast compared to other aperture settings.

Wide-open, at F2, and at F11 and above, the Sigma outperforms the Pentax 31mm by a hair.  The Pentax lens catches up by F2.8 and is sharper at F4. The two are neck-and-neck at F5.6 and F8.  F22 is not available on the Sigma lens.  Throughout the range, the 31mm pulls ahead in terms of micro-contrast.

Chart Test 2 - Corner Sharpness

Pentax 30mm
Pentax 31mm

F1.4

F1.8

http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6701.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6691.JPG
F2 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6702.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6692.JPG
F2.8 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6703.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6693.JPG
F4 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6704.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6694.JPG
F5.6 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6705.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6695.JPG
F8 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6706.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6696.JPG
F11 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6707.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6697.JPG
F16 http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6708.JPG http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6698.JPG
F22 --- http://www.pentaxforums.com/content/uploads/files/1/1034/IMGP6699.JPG

In the corners, the Sigma 30mm struggles compared to the Pentax lens, as is to be expected given that the latter is designed to cover a much larger image circle.  The Sigma becomes acceptably sharp by F5.6 and almost catches up to the 31mm at F8.  At F11 and F16 the Sigma is slightly better than the 31mm, though declining center sharpness at these aperture settings makes this advantage moot.

The test photos above also reveal the presence of prominent fringing and distortion in the corners of the Sigma lens.

Outdoor Test

In the following photos we compare the center sharpness of the 30mm to its corner performance.  All images are 100% crops.

Center
Corner
F1.4
F2
F2.8
F4
F5.6
F8
F11
F16

The real-world photos show that the best corner performance is between F4 and F11, and that center sharpness is excellent between F2 and F11 and superb between F2.8 and F5.6.

Sharpness Verdict

Although it struggles a bit in the corners, the new Sigma 30mm is an incredibly sharp lens comparable to Pentax's $1299 offering, the 31mm F1.8 Limited.  Considering its relatively-low price, the Sigma really impressed us in this area.


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