Lensbaby Burnside 35mm F2.8
In simple terms, vignetting is the darkening of the corners of an image that occurs at wider apertures. Every lens, wide open, will exhibit some. Most of the time, it need not be a problem for modern photographers. First, it is always possible to shoot at smaller apertures, mitigating the effect. Second, cameras released in the last few years often have built-in tools to remove vignetting in a way that's invisible to the user. Advanced software also often incorporates lens profiles which can seamlessly correct vignetting. Last, it is always possible to purchase higher-quality lenses that will show milder vignetting.
A fast lens is somewhat more likely to show vignetting than a slow one, although this is not a hard rule. A full frame lens also benefits from a sweet spot on APS-C, but shows its flaws more visibly on full frame cameras. A zoom is more likely to show vignetting at its wider focal lengths.
This section presents how the Burnside 35mm performs in regards to vignetting.
The test was performed by pointing the lens at a blank wall. Resulting files were scaled down, converted to grayscale for improved visibility, then exported. The following settings were used:
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The following chart summarizes the findings with the Burnside. The secondary iris was kept open; there is little point in closing it since it is designed to increase vignetting to create artistic effects.
Vignetting is of course more important with a full frame sensor. Wide open, it is approximately 1.3 EV, which will be noticeable if no correction is applied. The drop is rapid as the aperture closes, to stabilize near 0.5 EV at smaller apertures.
On APS-C, the results are much better, with a low value even at F2.8. Starting at F4 the effect will be hard to notice at around 0.2 EV.
The next images show the vignetting at various apertures for both sensor sizes. Click on any thumbnail to compare the vignetting at the given focal length.
Vignetting figures are excellent for APS-C sensors. On full frame sensors, F2.8 shows visible vignetting. Results improves significantly at F4 and below. Globally, the results are acceptable.
Note that we did not test the secondary aperture closed, as in this case of course vignetting is expected to occur.