Super-wide shootout---Sigma 12-24 vs K-M 17-35
Posted: Thu Jan 15, 2009 11:09 pm
Sigma AF 12-24 mm 1:4.5-5.6 EX DG vs Konica-Minolta AF 17-35 mm 1:2.8-4 (D)
A quick comparison on full 35-mm format (Sony A900)
At 12 mm
Sharpness
At 12 mm, the Sigma's sharpness is surpringly good in a wide area around the frame's center. Even f/4.5, which is the full aperture at 12 mm, is fully usable. Stopping down will improve sharpness as usual, but only by a minor degree. Optimal aperture for the frame's center is f/8; f/11 loses some sharpness due to diffraction.
Beginning at an image height (i. e. distance from center; utmost corner is 100 %) of approx. 75 %, or 16 mm, sharpness at wider apertures slowly starts to suffer. So near the corners, sharpness is best at f/11 which of course sacrifices some center sharpness. However the utmost corners appear blurred even at f/11 ... but that affects image heights beyond 96 % only, and mostly sagittal structures.
Lateral chromatic aberrations are very moderate. In Adobe Camera Raw, a setting of R/C -15 and B/Y ±0 or thereabouts will take care of it.
Distortion
At medium distance (approx. 2 m) there is clearly barrel-shaped distortion, but it's still acceptable for such an extreme angle of view. There is no hint of wave-form distortion (unlike the K-M at 17 mm) so it can be corrected in post-processing fairly easily. At infinity, the distortion is much lower than at medium distance---surprisingly low actually---so it will become noticable only in very critical applications. By the way, in most lenses distortion is lower at infinity and becomes worse at closer distances.
Vignetting
Boy---this lens does vignette! At 12 mm, that is. At full aperture, a smooth but firm vignetting starts out near the center, and then takes another sudden and serious rise right in the corners. When stopping down, each f-stop will reduce vignetting significantly, but even at f/11 some minor yet visible vignetting will remain.
For this angle of view, the cos^4 law predicts a natural vignetting of no less than 4.2 f-stops in the corners. Thanks to the highly asymmetrical retro-focus design, actual vignetting at smaller apertures is far less than that ... so we must consider yourselves lucky with this lens' small degree of residual vignetting. Remember---at 12 mm we really are on the far side of wide-angle territory.
At 17 mm
Sharpness
At a focal length of 17 mm the actual comparison sets in. And it's a mixed bag at 17 mm! Generally, the Sigma's performance is more even across the frame than the K-M's which is better at the center (mostly but not solely due to better contrast) but about equal to the Sigma at the edges. Actually the K-M's center sharpness is very impressive even at full aperture; optimum reached at f/5.6. And that's even though the K-M's lateral chromatic aberrations are about twice as strong as the Sigma's. By the way, the Sigma's CAs are of the red/cyan kind while the K-M's are magenta/green.
Overall, the K-M wins in the sharpness category at 17 mm. And even the full aperture---which is no less than f/2.8---is fully usable as far as sharpness is concerned; however that comes with some serious vignetting (see below).
Distortion
Big point for the Sigma here. The Sigma's distortion is a plain barrel-shape, and very low, almost zero. The K-M's is a nasty wave-form---mostly barrel-shaped at the central edges but with a pincushion twist towards the corners. The degree of the K-M's distortion, at medium distance, is about the same as the Sigma's at 12 mm but the shape is worse.
Vignetting
The K-M's vignetting at 17 mm and full aperture is about the same as the Sigma's at 12 mm and f/5.6---i. e. pretty strong. Stopping down will reduce vignetting significantly with every f-stop but even at f/8 some minor vignetting will remain. Only at f/11 it's gone completely. The Sigma's vignetting, at 17 mm, is very slighty stronger at each f-stop than the K-M's.
At 24 mm
Sharpness
With regard to sharpness, the situation at 24 mm is similar to that at 17 mm---except that the K-M's performance doesn't drop so much at the edges now. At the center, the K-M again is very strong even at full aperture, with an optimal aperture of f/5.6. At the frame's edges, the optimum is f/8. At the center, the Sigma is slightly weaker; at the corners it's pretty poor. Generally, the K-M at 24 mm (and by the way also at 28 mm but not at 35 mm) is virtually as good as most prime lenses.
Distortion
At 24 mm, distortion is virtually zero in both lenses.
Vignetting
At 24 mm, the K-M has only little vignetting. It's moderate at f/3.2, low at f/4, and virtually gone at f/5.6 and smaller. The Sigma, however, has surprisingly strong vignetting. At f/5.6 it's slightly stronger than the K-M's at f/3.2; at f/8 it's about the same as the K-M's at f/3.2.
Resumee
At 12 mm on 35-mm full-frame format, the Sigma 12-24 simply has no competition, and it does perform well enough for serious work. So despite a few shortcomings (which are typical for super-wide lenses) it definitely is not just a 122° toy to evoke a few ohs and ahs but a worthwhile tool.
However at 17 mm it is slightly inferior to the K-M 17-35, and at 24 mm it is clearly inferior. So it should be purchased for the 12 mm short end; the rest of the focal range unfortunately is not quite as useful as it could be.
-- Olaf
A quick comparison on full 35-mm format (Sony A900)
At 12 mm
Sharpness
At 12 mm, the Sigma's sharpness is surpringly good in a wide area around the frame's center. Even f/4.5, which is the full aperture at 12 mm, is fully usable. Stopping down will improve sharpness as usual, but only by a minor degree. Optimal aperture for the frame's center is f/8; f/11 loses some sharpness due to diffraction.
Beginning at an image height (i. e. distance from center; utmost corner is 100 %) of approx. 75 %, or 16 mm, sharpness at wider apertures slowly starts to suffer. So near the corners, sharpness is best at f/11 which of course sacrifices some center sharpness. However the utmost corners appear blurred even at f/11 ... but that affects image heights beyond 96 % only, and mostly sagittal structures.
Lateral chromatic aberrations are very moderate. In Adobe Camera Raw, a setting of R/C -15 and B/Y ±0 or thereabouts will take care of it.
Distortion
At medium distance (approx. 2 m) there is clearly barrel-shaped distortion, but it's still acceptable for such an extreme angle of view. There is no hint of wave-form distortion (unlike the K-M at 17 mm) so it can be corrected in post-processing fairly easily. At infinity, the distortion is much lower than at medium distance---surprisingly low actually---so it will become noticable only in very critical applications. By the way, in most lenses distortion is lower at infinity and becomes worse at closer distances.
Vignetting
Boy---this lens does vignette! At 12 mm, that is. At full aperture, a smooth but firm vignetting starts out near the center, and then takes another sudden and serious rise right in the corners. When stopping down, each f-stop will reduce vignetting significantly, but even at f/11 some minor yet visible vignetting will remain.
For this angle of view, the cos^4 law predicts a natural vignetting of no less than 4.2 f-stops in the corners. Thanks to the highly asymmetrical retro-focus design, actual vignetting at smaller apertures is far less than that ... so we must consider yourselves lucky with this lens' small degree of residual vignetting. Remember---at 12 mm we really are on the far side of wide-angle territory.
At 17 mm
Sharpness
At a focal length of 17 mm the actual comparison sets in. And it's a mixed bag at 17 mm! Generally, the Sigma's performance is more even across the frame than the K-M's which is better at the center (mostly but not solely due to better contrast) but about equal to the Sigma at the edges. Actually the K-M's center sharpness is very impressive even at full aperture; optimum reached at f/5.6. And that's even though the K-M's lateral chromatic aberrations are about twice as strong as the Sigma's. By the way, the Sigma's CAs are of the red/cyan kind while the K-M's are magenta/green.
Overall, the K-M wins in the sharpness category at 17 mm. And even the full aperture---which is no less than f/2.8---is fully usable as far as sharpness is concerned; however that comes with some serious vignetting (see below).
Distortion
Big point for the Sigma here. The Sigma's distortion is a plain barrel-shape, and very low, almost zero. The K-M's is a nasty wave-form---mostly barrel-shaped at the central edges but with a pincushion twist towards the corners. The degree of the K-M's distortion, at medium distance, is about the same as the Sigma's at 12 mm but the shape is worse.
Vignetting
The K-M's vignetting at 17 mm and full aperture is about the same as the Sigma's at 12 mm and f/5.6---i. e. pretty strong. Stopping down will reduce vignetting significantly with every f-stop but even at f/8 some minor vignetting will remain. Only at f/11 it's gone completely. The Sigma's vignetting, at 17 mm, is very slighty stronger at each f-stop than the K-M's.
At 24 mm
Sharpness
With regard to sharpness, the situation at 24 mm is similar to that at 17 mm---except that the K-M's performance doesn't drop so much at the edges now. At the center, the K-M again is very strong even at full aperture, with an optimal aperture of f/5.6. At the frame's edges, the optimum is f/8. At the center, the Sigma is slightly weaker; at the corners it's pretty poor. Generally, the K-M at 24 mm (and by the way also at 28 mm but not at 35 mm) is virtually as good as most prime lenses.
Distortion
At 24 mm, distortion is virtually zero in both lenses.
Vignetting
At 24 mm, the K-M has only little vignetting. It's moderate at f/3.2, low at f/4, and virtually gone at f/5.6 and smaller. The Sigma, however, has surprisingly strong vignetting. At f/5.6 it's slightly stronger than the K-M's at f/3.2; at f/8 it's about the same as the K-M's at f/3.2.
Resumee
At 12 mm on 35-mm full-frame format, the Sigma 12-24 simply has no competition, and it does perform well enough for serious work. So despite a few shortcomings (which are typical for super-wide lenses) it definitely is not just a 122° toy to evoke a few ohs and ahs but a worthwhile tool.
However at 17 mm it is slightly inferior to the K-M 17-35, and at 24 mm it is clearly inferior. So it should be purchased for the 12 mm short end; the rest of the focal range unfortunately is not quite as useful as it could be.
-- Olaf
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