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Falloff of Illumination (Corner Darkening)
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Nikon 12-24mm Tokina 12-24mm Sigma 10-20mm Tamron 11-18mm

Nikon 12 - 24 mm f/4, Tokina 12 - 24 mm f/4, Sigma 10 - 20 mm f/4 - 5.6 and Tamron 11 - 18 mm f/4.5 - 5.6.
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Most lenses get darker in the corners at large apertures. This is caused by mechanical vignetting inside the lens. This goes away as the lens is stopped down.

Even if a lens has falloff it's not a bad thing. Ansel Adams deliberately darkened the edges and corners of his prints to focus your attention. He called this "edge burning." This falloff can be used quite creatively with ultrawide lenses. Learn your lens and use it to your advantage.

Even the worst of these are much better than the best manual focus ultrawide fixed focal length lenses of 20 years ago. None of these zooms has strong falloff at any setting. My older lenses would usually get pretty dark in the corners wide open. None of these do.

All these lenses are retrofocus and well corrected for cos^4 falloff stopped down. I list below the f/stops needed to eliminate any falloff.

10 mm
Almost none. Gone by f/5.6 - 8.
11 mm
12 mm
Mild. Gone by f/5.6.
Moderate. Almost gone at f/5.6 and gone by f/8.
14 mm
Moderate. Mostly gone by f/11.
Mild. Gone by f/8.
15 mm
18 mm
Mild to moderate. Gone by f/5.6.
Mild. Gone by f/5.6.
Moderate. Mild @ f/8, gone by f/11.
20 mm
Moderate. Improves and much less by f/11 but still not entirely gone.
24 mm
Moderate. Gone by f/5.6.
Best at wide end of zoom. Completely gone by f/5.6.
Best at long end of zoom. Almost entirely gone at f/5.6.
Oddly takes 2 or three stops to go away completely. Requires f/11 at mid to longer ranges to eliminate.
Best at wide end of zoom. Requires f/8 to f/11 for complete elimination at longer end.

Next: Filters and Vignetting


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