Pentax SMC-FA* 24mm f/2 AL [IF] - Review / Lab Test Report - Analysis
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The FA* 24mm f/2 exhibits a fairly low degree of barrel distortion (1.5%) which is better than average for a lens in this class.

The chart above has a real-world size of about 120x80cm.


As a full format lens the FA* 24mm f/2 benefits from the usual sweet spot effect on APS-C DSLRs. However, it is also an ultra-large aperture lens so it does still produce quite high degree of vignetting at f/2 (0.89EV) even within this scope. The problem is negligible from about f/4 onwards.

MTF (resolution)

Pentax users may be aware of Bojidar Dimitrov website where he mentions that the user feelings about this lens are a bit mixed. Well, I can certainly concur here. The FA* 24mm f/2 produced a fairly similar resolution characteristic like the recently tested Sigma AF 30mm f/1.4 EX DC.

The Pentax lens has a very sharp center performance straight from f/2. However, the border quality is fairly dismal here. This doesn't really change till about f/4 where the border resolution finally reaches good levels. The center resolution peaks at f/5.6 with absolutely superb figures whereas the borders require f/8 to reach very good quality.

It is worth to mention that the lens seems to produce a very high degree of contrast even at f/2. "Sharpness" is a combination of resolution and contrast so subjectively the image results may appear better than suggested by the graphs - probably one of the reasons for the varying user impressions out there.

Please note that the MTF results are not directly comparable across the different systems!

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 not a a real strong point of the FA* 24mm f/2. The problem reaches an average pixel width of around 1.2px at the image borders. This is not a worryingly high degree but noticeable at times.


The Pentax SMC-FA* 24mm f/2 AL [IF] is an interesting lens but not a really stellar performer as you may expect from its FA* designation. The resolution characteristic has a very strong emphasis on the center resolution whereas the border quality is a bit substandard especially at large aperture settings. The delivered contrast seems very high even at f/2 which may compensate some of the shortcomings on side of the sheer resolution. The level of distortions is comparatively low for such as lens whereas vignetting and CAs are about average. The build quality of the lens is very good although today's Pentax Limited lenses are on par or even better in this respect.

Optical Quality:
Mechanical Quality:

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