Sigma AF 24mm f/2.8 macro (Pentax K) - Review / Lab Test Report - Analysis
Lens Reviews - Pentax
Article Index
Introduction
Analysis

Distortion

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.

Vignetting

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 negligible.

MTF (resolution)

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 Imatest Explanations

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.

Verdict

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.

Optical Quality:
Mechanical Quality:
Price/Performance:discontinued



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