Olympus M.Zuiko Digital ED 8-25 mm f/4 PRO
8. Vignetting
| E-M5 II, JPEG, 8 mm, f/4.0 | E-M5 II, JPEG, 8 mm, f/5.6 |
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| E-M5 II, JPEG, 16 mm, f/4.0 | E-M5 II, JPEG, 16 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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At a difficult combination of the 8 mm focal length and the maximum relative aperture vignetting amounts to 29% (-1.01 EV) so it would be difficult to call it high. By f/5.6 it reaches a level of 21% (-0.67 EV), by f/8.0 it decreases to 17% (-0.53 EV), and then it stops reacting on further stopping down at all.
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Noticeably better situation can be observed at 16 mm where, by f/4.0, brightness loss in the frame corners gets to 17% (-0.53 EV). By f/5.6 it drops to a level of 13% (-0.40 EV) and further stopping down decrease vignetting just slightly, by another percent.
Similar situation can be observed at 25 mm. Here, at the maximum relative aperture, we got a result of 19% (-0.61 EV), by f/5.6 light fall-off decreased to 15% (-0.47 EV), and by f/8.0 it dropped to 12% (-0.38 EV).
Now let's check the situation on RAW files developed with independent software.
| E-M5 II, RAW, 8 mm, f/4.0 | E-M5 II, RAW, 8 mm, f/5.6 |
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| E-M5 II, RAW, 16 mm, f/4.0 | E-M5 II, RAW, 16 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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At the widest angle of view and the maximum relative aperture vignetting reaches a quite significant level of 43% (-1.61 EV), being distinctly higher than the same value but on JPEG files. A distortion correction on a level of -6.4% has to involve significant image cropping.
By f/5.6 vignetting decreases to a level of 31% (-1.07 EV), and by f/8.0 to 23% (-0.75 EV). By f/11.0 and f/16.0 apertures we got the same result, reaching 20% (-0.64 EV).
In the middle of the focal range vignetting levels on RAW files are practically the same as the results measured on JPEGs. It shouldn't surprise you because distortion is zero at that point so it doesn't have to be corrected and, as a result, images aren't cropped almost at all. By f/4.0 vignetting amounts to 18% (-0.58 EV), just 1% higher than the result we obtained on JPEG files. By f/5.6 light fall-off decreases to 14% (-0.45 EV), and by f/8.0 it gets even lower, dropping to 12% (-0.37 EV). Further stopping down doesn't have any measureable influence on the aberration described in this chapter.
At 25 mm focal length there are not many problems either: by f/4.0 vignetting keeps a moderate level of 20% (-0.66 EV), by f/5.6 it decreases to 16% (-0.52 EV), and by f/8.0 - to 13% (-0.40 EV).
Overall you can say the tested lens doesn't have any serious vignetting problems. They appear only when you want to reach an angle of view wider than declared and use uncorrected RAW files at the 8 mm focal length. In other cases, no matter whether you save your images as JPEG or RAW files, vignetting won't be especially bothersome. In the era of mirrorless cameras such luxury is available only in the Micro 4/3 system.
| Olympus O-MD E-M5 Mark II, RAW, 8 mm, f/4.0 |
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| Olympus O-MD E-M5 Mark II, RAW, 16 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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