Fujifilm Fujinon XF 18-55 mm f/2.8-4 OIS
8. Vignetting
As you see the problems are really negligible. At 18 mm focal length and by f/2.8 the vignetting reaches a slight level of 13% (-0.41 EV). The result by f/4.0, amounting to 15% (-0.48 EV) so a tad higher, proves that the aberration is corrected there; if there was no interference, according to physical laws with the stopping down the vignetting was bound to decrease. At 18 mm focal length we don’t observe such a thing.
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Similar situation can be observed in the middle of the focal range. By f/3.2 the brightness loss in frame corners is 11% (-0.35 EV), on stopping down to f/4.0 it increases to 13% (-0.40 EV) and by f/5.6 it decreases to 9% (-0.29).
At the maximum focal length for all apertures ranging from f/4.0 to f/8.0 the vignetting is, within the margin of error, the same, amounting to 15% (-0.46 EV); only by f/11 you can see it decreasing to 9% (-0.28 EV).
Let’s check now how the vignetting looks on uncorrected RAW files.
There are no miracles there – the vignetting behaves in full accordance with physical laws, decreasing on stopping down.
The worst result we noticed at the most difficult combination of the wide angle and f/2.8 where the vignetting reaches as much as 45% (-1.75 EV). After stopping down it decreases to 33% (-1.18 EV). The problem becomes moderate by f/5.6 where the vignetting gets to 28% (-0.94 EV). Further stopping down doesn’t influence that aberration in a significant way – by f/8 and by f/11 it is 22% (-0.72 EV).
In the middle of the focal range the situation is noticeably better but it would be difficult to say that there are no problems at all. By f/3.2 the light fall-off in the corners of the frame reaches 39% (-1.41 EV) and it decreases to 29% (-1.0 EV) by f/4.0. The end of serious problems can be observed by f/5.6 where the vignetting is 18% (-0.58 EV). By f/8.0 it decreases to 16% (-0.52 EV) and further stopping down doesn’t have any measurable influence on the aberration described in this chapter.
At 55 mm the vignetting increases again. At the maximum relative aperture it is 42% (-1.60 EV) and it decreases to 28% (-0.94 EV) by f/5.6. When it comes to f/8.0 and f/11.0 relative apertures the vignetting amounts to 21% (-0.69 EV) and 15% (-0.49 EV) respectively.
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