Construction and autofocus
The Sigma 12-24 mm lens is made of a high quality type of plastic and the fitting is made of metal. The zoom ring is without play, but makes a squeaky sound when turning. The focal ring has just the right friction and turns without play. Attached to the lens is a kind of flower shaped lens hood, which can be extended using an APS-C camera. Assembling a filter on the front is not possible.
The autofocus is done by means of a very quiet HSM drive. Focusing with a Canon 60 D from 15 meters to 1.5 meters lasts 0.15 seconds with a focal length of 24 mm. That is a very short time. The camera does not hunt at low light despite the low luminosity.
The vignetting of the Sigma 12-24 mm in stops is on the high side at full aperture at all focal lengths. This lens error can be controlled well with the right software.
Distortion Sigma 12-24 mm
The distortion measured in Sigma 12-24 mm jpg files, expressed as a percentage, is large at a focal length of 12 mm, namely -2.2%. At a focal length of 18 mm and 24 mm, the distortion is much lower. Distortion can be controlled with the appropriate software.
The blurry rings all get a circle, making the imagae ‘busy’. The bokeh of the Sigma 12-24 mm lens is not so pretty. Due to the small sensor and the small initial aperture, one cannot play with the depth of field.
The lens is fairly insensitive to flare at backlight. Ghosting does appear somewhat.
Resolution Sigma 12-24 mm
The resolution, expressed in line pairs/sensor height, reaches high levels at the center at 12 mm, 18 mm and 24 mm immediately at full aperture. This Sigma is not a very fast lens but can be used at full aperture immediately and by stopping down, the image does not get sharper. At 24 mm, the resolution then decreases. It is best to use the aperture values f/4.5 – f/5.6 unless more depth of field is needed.
We came across a big difference in corner resolution at the test of this Sigma on the full frame camera Canon 5D MK2. The right corner below is far less sharp than the other corners at that combination. That difference in depth is much smaller when using a Canon 60D, which is equipped with an APS-C sensor.@f/9.0, 12 mm
Chromatic aberration Sigma 12-24 mm
At a focal length of 18 mm, the chromatic aberraion of the Sigma 12-24 mm is high and will have to be controlled by software.
- High resolution, also with full aperture
- Minor glare at backlight
- Very fast AF
- Suitable for full frame sensor and APS-C format sensor
- Good workmanship
- Much distortion at 12 mm
- Much vignetting at full aperture
- Large, heavy and pricy compared to lenses that are only suitable for APS-C sensor format