Sony FE 28 mm f/2
8. Vignetting
| A7R II, APS-C, f/2.0 | A7R II, APS-C, f/2.8 |
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The light fall-off in the frame corners is noticeable without any problems. At the maximum relative aperture it amounts to a significant value of 37% (−1.32 EV) . Fortunately already by f/2.8 and f/4.0 it drops to moderate levels of 15% (−0.46 EV), and 14% (−0.43 EV) respectively.
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After passing to a bigger full frame sensor there are much more problems and photos, shown below, are the proof.
| A7R II, FF, f/2.0 | A7R II, FF, f/2.8 |
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| A7R II, FF, f/4.0 | A7R II, FF, f/5.6 |
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At the maximum relative aperture we experienced as much as 67% (−3.22 EV) of brightness loss. It is obvious small dimensions of the lens, its good aperture fastness, wide angle of view, joined with a small distance between the rear element and the huge sensor contribute to that really weak result. For example the Batis 2/25, tested on the same sensor, performed better, with vignetting of 62% even if its task was more difficult because of its bigger angle of view.
Stopping down helps to limit the vignetting but is not as effective as we wish it were. By f/2.8 the brightness loss in the frame corners still amounts to 47% (−1.84 EV), by f/4.0 it decreases to 34% (−1.21 EV), and by f/5.6 it drops to 31% (−1.06 EV). Further stopping down doesn't have any measureable influence on this aberration.
| Sony A7R II, JPEG, f/2.0 |
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Below we present averaged out values of brightness loss shown in concentric circles as you move further away from the frame centre. The numerical value for every image, expressed in percents, shows the area limited from the top and right by 100% and from the bottom by the presented curve. The area indicates how much light overall is lost due to the vignetting effect. Please don’t mix these percentages with the values given at the beginning of the chapter because they aren’t directly connected.
