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Lens review

Sigma A 40 mm f/1.4 DG HSM

10 December 2018
Maciej Lata││o

8. Vignetting

First let’s check how the Sigma A 1.4/40 performs in this category on the smaller sensor of the Canon 50D – below you can find the appropriate thumbnails.

Canon 50D, f/1.4 Canon 50D, f/2.0
Sigma A 40 mm f/1.4 DG HSM - Vignetting Sigma A 40 mm f/1.4 DG HSM - Vignetting


There are no reasons to get worried. At the maximum relative aperture the vignetting is 25% (−0.84 EV); by f/2.0 and f/2.8 it decreases to an imperceptible value of, respectively, 9% (−0.29 EV) and 6% (−0.19 EV).

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Now let’s check how the situation changes when you pass to full frame – below we present images from the Canon EOS 5D Mark III.

Canon 5DáIII, f/1.4 Canon 5DáIII, f/2.0
Sigma A 40 mm f/1.4 DG HSM - Vignetting Sigma A 40 mm f/1.4 DG HSM - Vignetting
Canon 5DáIII, f/2.8 Canon 5DáIII, f/4.0
Sigma A 40 mm f/1.4 DG HSM - Vignetting Sigma A 40 mm f/1.4 DG HSM - Vignetting


Here the vignetting is much more pronounced. At the maximum relative aperture it reaches 59% (−2.56 EV) and, taking huge physical dimensions of the lens into account, it is a weak result. It is true that the Sigma A 1.4/35 fared even weaker in this category but the A 1.4/50 model was better. Of course you have to remember that the size of the lens is just one of vignetting factors; you can control that aberration better in bigger lenses but if the instrument is also optically complex the task might be not so easy after all. You have to take into account light absorption effects in big blocks of glass and a weaker efficiency of anti reflection coatings when the light falls at more acute angles. When there is a lot of air-to-glass surfaces, and such is the situation of the Sigma A 1.4/40, the losses of light in the corners might be significant.

Fortunately vignetting decreases swiftly with the stopping down. By f/2.0 we got a result of 35% (−1.26 EV), and by f/2.8 it amounted to 17% (−0.53 EV). From the f/4.0 aperture upwards the vignetting disappeared practically completely, being officially 11% (−0.34 EV).

Canon 5DáIII, JPEG, f/1.4
Sigma A 40 mm f/1.4 DG HSM - Vignetting