Venus Optics LAOWA 9 mm f/5.6 FF RL
8. Vignetting
| A7R II, APS-C, f/5.6 | A7R II, APS-C, f/8.0 |
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At the maximum relative aperture brightness loss in frame corners amounts to 33% (−1.14 EV), so it will be perfectly visible. On stopping down the aperture to f/8.0 that aberration decreases slightly to a value of 31% (−1.06 EV) and it can be reduced by another percent if you stop the lens down to f/11.0.
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After passing to a bigger full frame sensor there are more problems and you can spot them with ease in photos shown below.
| A7R II, FF, f/5.6 | A7R II, FF, f/8.0 |
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| A7R II, FF, f/11.0 | A7R II, FF, f/16.0 |
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The result reached at the maximum relative aperture amounts to as much as 72% (−3.68 EV) and we think two factors contributed to that value. Firstly of course the parameters of the lens. Secondly and more importantly, the specificity of the mount and other aspects connected to that, like telecentricity (or rather lack thereof) and the fact that the rear element throws light at huge angles toward pixels of the sensor. A lot of light get lost just because of these angles; if you tested the Laowa on an optical bench, independently of the sensor, vignetting would have been lower for sure. Still nobody takes photos with a lens positioned on an optical bench...
The performance of the lens on stopping down confirms that huge vignetting is a result of cooperation between optics and the sensor and not just optics on its own. Brightness loss decreases but not especially fast – by f/8.0 it reaches 69% (−3.37 EV), by f/11.0 it drops to 64% (−2.98 EV), and by f/16.0 it gets to a still very high level of 60% (−2.66 EV).
| Sony A7R II, JPEG, f/5.6 |
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