Sigma AF 50mm f/1.4 EX DG HSM (Canon) - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)
Friday, 15 August 2008 20:00

Distortion

The Sigma produces a fairly typical degree of barrel distortion (0.6%) for a 50mm lens - this is usually not disturbing in field conditions.

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

Vignetting

As mentioned the Sigma has a fairly massive front element which is already an indicator for a very good vignetting characteristic - more so on APS-DSLR due to the sweet spot effect here. Within this scope the Sigma has a comparatively moderate vignetting of 0.63EV at max. aperture which may be visible at times. The problem is pretty much negligible from f/2 onwards.

MTF (resolution)

The Sigma produced very good to excellent resolution figures in the MTF lab. At f/1.4 the center as well as the borders are already on a very good level which is quite unusual - typically there's a higher spread here (in this class). The center quality improves to outstanding levels when stopping down a little - the lens has probably the potential to beat the 8mp sensor resolution of the test camera at medium aperture settings. The borders improve more gradually and it takes f/5.6 till they reach excellent levels (just). It seems as if the primary design objective circled around the performance at very large apertures which makes naturally sense for such a lens. The field curvature is negligible.

In the field the lens has a few troubles at extremely close focus distances and large aperture settings - this is forgivable regarding the impressive performance at mainstream focus distances.

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 generally moderate with an average pixel width around 0.7px at the image borders.

Bokeh

The quality of the bokeh (out-of-focus blur) is a primary aspect for such a large aperture lens and the Sigma lens is capable of producing very decent results here. The rounded aperture shape in out-of-focus highlights remains intact all the way up to f/4. However, at f/1.4 there're also traces of onion-like structures here. The general foreground and background blur can also be somewhat nervous at f/1.4 but this aspect is pleasing again from f/2 onwards.

Longitudinal (Axial) Chromatic Aberrations (LoCA)

LoCAs (non-coinciding focal planes of the various colors), sometimes called "bokeh CAs", are a general problem in this lens class. As you can notice below the halos have different colors - magenta (red + blue) in front the focus point and green beyond. The Sigma does a comparatively good job here though. The problem is visible but although not overly disturbing at f/1.4 and at f/2 it is usually not field-relevant anymore.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/1.4 f/2 f/2.8 f/4




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