At the time of writing, I have yet to receive the demo unit of the newly launched Sigma 12-24mm F4.0 DG HSM | Art, so many would wonder how this lens performs on the sd Quattro H with the larger APS-H sized sensor. It certainly performs admirably on the sd Quattro (APS-C) without a single doubt with center resolution and sharpness exceeding even some of the primes available today. Corner sharpness on APS-C is very good, which matches to the center from F2.8 onwards, although it is still acceptable at wide open. It all depends on the subject on which this lens is used on. It is acceptable for corner performance to degrade slightly (with a tad of vignette) for portraiture work. For landscape, I would prefer to use it at F4.0-5.6 or even to F8 if a deeper depth of field is required. The MTF chart peaks at this range of apertures.
Even when the lens is used on the H without turning on DC Crop, the center resolution and sharpness are simply amazing! Before I go deeper into that, let’s compare how the rendering differs between the APS-C and APS-H when the field of view is matched :
At a glance it does seem that the H renders the image with less barrel distortion. This is true as it uses 21mm to produce a field of view of 28mm vs 18mm required on the APS-C. Interesting isn’t it?
If the same focal length is used, the resulting image on both sensors will be as below (simulated with DC Crop Off and On):
Let’s move on…
I just mentioned that the lens performs flawlessly in the center or rather across 60% of the frame. It can definitely out-resolve the H sensor, although it is kind of expected because the size of the sensels on both the Foveon (APS-C and APS-H) are essentially the same. However, one would gain much from the better resolving power on the H when the frame and field of view are similar due to the 30% increased in megapixels.
Perhaps the issue at hand which concerns us is how this lens performs at the corners. Well, it is not too pretty neither is it bad. The chromatic aberration and fringing can yield its ugly head when the contrast is high.
Sigma Photo Pro is able to mitigate or at times completely eliminate this by turning on :
- CA Correction >> Lens Profile (may need to set it higher than 1.0 for severe cases)
- Fringe Correction, activating both Green and Magenta correction
The settings are straight forward and are usually sufficient to perform the correction.
In more severe cases, I would prefer to retouch them manually in Photoshop or Lightroom.
Corner sharpness degrades visibly because the APS-H sensor occupies a larger part of image circle projected by the lens. This is not a fault by design as the lens is not rated for use on the sd Quattro H, at least not something Sigma would recommend to use on the H. A much better choice is definitely the new 12-24 F4 Art which covers a full frame sensor. Please feel free to download the file below:
Redeveloped with the following adjustments in Sigma Photo Pro:
- CA Correction & Fringe Correction
- Luminance & Color Noise Reduction minimum (left-most setting)
- Detail + 2 (to try and compensate for the reduced sharpness at the corners)
There are indeed improvements as the focal length increases. I leave it to you to draw your own conclusions.