of Illumination (Corner Darkening)
© 2006 KenRockwell.com
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.
Click an image to get it from Adorama. Also try Amazon. It helps me if you get yours at either one.
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.
Next: Filters and Vignetting