Olympus M.Zuiko Digital ED 12-45 mm f/4.0 PRO
8. Vignetting
| E-M5 II, JPEG, 12 mm, f/4.0 | E-M5 II, JPEG, 12 mm, f/5.6 |
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| E-M5 II, JPEG, 25 mm, f/4.0 | E-M5 II, JPEG, 25 mm, f/5.6 |
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| E-M5 II, JPEG, 45 mm, f/4.0 | E-M5 II, JPEG, 45 mm, f/5.6 |
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In the case of the combination of 12 mm focal length and f/4.0 aperture you have to take into account a loss of 29% of ligh in frame corners (-1.00 EV). Stopping down the apertue to f/5.6 allows you to diminish that loss to 22% (−0.71 EV), and employing the f/8.0 aperture makes vignetting decrease further to 16% (−0.50 EV). Results reached by f/11.0 and f/16.0 are the same, amounting to 12% (−0.38 EV).
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In the middle of the focal range vignetting is distinctly lower and at the maximum relative aperture it reaches just 14% (−0.45 EV). On stopping down the aperture to f/5.6 it becomes practically imperceptible, being just 9% (−0.29 EV).
A slight increase of vignetting can be perceived at the maximum relative aperture where, by f/4.0, it gets to 19% (−0.62 EV). Like previously, the f/5.6 aperture is able to eliminate the problem practically completely as light fall-off decreases to a value of just 7% (−0.22 EV).
In the distortion chapter we mentioned that the lens doesn't manage to control that aberration at all, allowing software of the camera to correct it instead. It is done at a cost – images have to be cropped so, at the shortest focal lengths, areas with the highest vignetting are simply removed. Now let's check the vignetting level on RAW files – appropriate thumbnails can be found below.
| E-M5 II, RAW, 12 mm, f/4.0 | E-M5 II, RAW, 12 mm, f/5.6 |
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| E-M5 II, RAW, 25 mm, f/4.0 | E-M5 II, RAW, 25 mm, f/5.6 |
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| E-M5 II, RAW, 45 mm, f/4.0 | E-M5 II, RAW, 45 mm, f/5.6 |
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According to our expectations, the results at 12 mm are now noticeable higher. By f/4.0 you deal with a distinct level of 46% (−1.76 EV), which decreases to 40% (−1.48 EV) on stopping down the aperture to f/5.6. Further reduction of the relative aperture doesn't influence vignetting so much. By f/8.0 that aberration reaches 38% (−1.40 EV), by f/11.0 it amounts to 36% (−1.30 EV), and by f/16.0 it is close to a still noticeable value of 33% (−1.14 EV).
At longer focal lengths, with lower distortion levels, results of our measurements for RAW files are just slightly higher than respective values we got on JPEG files. Differences reach just 1-2% so are on the borderline of measuring error.
Using the 25 mm focal length and f/4.0 aperture you have to take into account vignetting of 15% (−0.47 EV), which decreases to 10% (−0.31EV), when you stop down the aperture to f/5.6.
At the maximum focal length and f/4.0 aperture light fall-off in the frame corners amounts to 21% (−0.67 EV) and it decreases to an imperceptible value of 8% (−0.24 EV) on stopping down the aperture to f/5.6.
| Olympus O-MD E-M5 Mark II, RAW, 12 mm, f/4.0 |
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| Olympus O-MD E-M5 Mark II, RAW, 25 mm, f/4.0 |
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| Olympus O-MD E-M5 Mark II, RAW, 45 mm, f/4.0 |
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