Sigma C 15 mm f/1.4 DC
8. Vignetting
| A7R IIIa, FF, f/1.4 | A7R IIIa, FF, f/8.0 |
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Now let's check how the Sigma C 15 mm f/1.4 DC corrects vignetting on the APS-C/DX sensor. First, we are going to analyze uncorrected JPEG files – appropriate thumbnails are presented below.
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| A7R IIIa, APS-C, f/1.4 | A7R IIIa, APS-C, f/2.0 |
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| A7R IIIa, APS-C, f/2.8 | A7R IIIa, APS-C, f/4.0 |
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At the maximum relative aperture, the vignetting is very high, reaching a level of as much as 64% (-2.98 EV). Of course, you can always notice that the more expensive Sony model on uncorrected files fared even weaker, as its result amounted to 66%. On the other hand, vignetting is actually the first testing category where the new Sigma is defeated distinctly by its predecessor, as in its case vignetting reached 43%. Still, the older lens had it easier because of a narrower angle of view and bigger physical dimensions.
Stopping down the aperture to f/2.0 decreases vignetting to a still significant level of 48% (-1.88 EV). Also, by f/2.8 you won't have any problems noticing it, as it amounts to 31% (-1.06 EV). More or less sensible values can be observed from f/4.0, where we determined a value of 22% (-0.74 EV). By f/5.6 we got a result of 19% (-0.60 EV). Further stopping down doesn't bring any measureable effects.
| Sony A7R IIIa, APS-C, JPEG, f/1.4 |
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It's also worth checking the vignetting level on corrected JPEG files because you deal there with a field of view amounting to 90 deg and completely distortion-free. Appropriate thumbnails can be found below.
| A7R IIIa, APS-C, f/1.4 | A7R IIIa, APS-C, f/2.0 |
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| A7R IIIa, APS-C, f/2.8 | A7R IIIa, APS-C, f/4.0 |
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This time, at the maximum relative aperture, this aberration reaches 58% (-2.48 EV). By f/2.0 vignetting decreases to 39% (-1.43 EV), by f/2.8 to 23% (-0.77 EV), and by f/4.0 it reaches a not especially bothersome level of 16% (-0.68 EV), and by f/5.6 it drops to 15% (-0.47 EV). Further stopping down doesn't bring any measureable effects.
