Here’s an effect we forget sometimes. When a lens is wide open, it vignettes.
My 50mm lens at f/1.2:
And here is that same lens a stop and a third closed down, at f/2.0:
Can you see the difference? The first picture, wide open, shows significantly more vignetting.
Now I like vignetting – a lot, in portraits. But shooting portraits with a lens wide open is rather dangerous, since depth of field is very shallow and may not be sufficient. So I add vignetting in Lightroom – Post Crop Vignetting is one of the best controls in Lightroom for when you are shooting portraits.
And when you are not shooting portraits, avoid vignetting like this – so in those cases, avoid shooting with your fast lens wide open.
Interesting Michael; my 85mm f/1.2 does not vignette at all fully open… I have used it all through the shots I took of the most recent photo shootout in the SoCal Photogs group; you can see some of the pictures on my blog here: http://blog.stantonphotostudios.com/?p=389 and while most have some sort of post processing, none for removing vignette and all were taken in bright daylight in full sun with wide open f/1.2
I wonder if it is your camera.. I think the 1D Mark III is not a full sensor… right? Perhaps you are getting the vignette form the camera.. although I shot these pictures of the “gypsies” with my 7D since I just sold my old 5D Mark II and the new one did not arrive in time for the shootout… and the 7D is also a crop sensor…