Sigma AF 24mm f/2.8 macro (Pentax K) - Review / Lab Test Report - Analysis
Lens Reviews -
Tuesday, 25 December 2007 20:35
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The Sigma shows its fair share of barrel distortion (~2%). While this isn't overly
impressive for a fix-focal lens it is also quite typical for a lens in this class.
The chart above has a real-world size of about 120x80cm.
Despite its full format origins the Sigma shows a quite pronounced degree of vignetting
at f/2.8 (0.9EV). As usual it helps to stop down but it takes f/5.6 till the problem is
The Sigma AF 24mm f/2.8 macro produced very good to excellent resolution figures in the
MTF lab. At wide-open aperture the center performance is already very high followed by
good quality at the borders. Stopping down results in a gradual improvement till the
peak resolution is reach at f/8 with an excellent center and very good borders.
Typical for most lenses diffraction effects start to reduce the quality from f/11 onwards.
Below is a simplified summary of the formal findings. The chart shows line widths
per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding
Chromatic Aberrations (CAs)
Lateral chromatic aberrations (color shadows at harsh contrast transitions) are
fairly well-controlled for a lens in the focal length class. In absolute terms
CAs are getting more obvious from about f/5.6 with an average CA width around
1.3px at the image borders.
The Sigma AF 24mm f/2.8 macro is capable to deliver a very solid performance
which is still up to the current quality standards. The resolution is already
high at f/2.8 and improves further up to excellent (center) and very good (border)
levels at f/8. The distortion and CA characteristics are about average for a lens
in this class. The vignetting at large apertures could be a bit better especially
considering that this is a full format lens used on an APS-C DSLR. The build quality
is very fine and the AF performance leaves nothing to be desired. As mentioned you
will not be able to find the Sigma in shops anymore but it is quite frequently
offered on the used market for quite low prices. If you're looking for a moderate
wide-angle fix-focal lens the Sigma could still be worth a deeper look.