"Here’s what you need to know about the auto focus systems and aperture in order for this test to make sense. When slr’s or slt’s like the a77 are trying to focus, the aperture of the lens is always open to widest aperture until the shutter button is pressed. Then the camera then adjusts the aperture to whatever setting you have, and takes the picture. This all happens in a micro-second as you would imagine.
You may have noticed this about the aperture on some cameras when using the DOF (depth of field) preview button. What that button does is set the aperture to the actual value you have set, hence giving you an accurate depth of field preview."
P.S The new, Serious and more business conscious Ken Rockwell appears to have changed the wording, the context, heck, everything in his review of this camera. It is no longer "less responsive than his kids toys", and not worse of all Nikon DSLRs ever made. It (the Canon EOS 5D Mark II) is now better than any Nikon at almost everything, and overall, one of the best cameras ever made. Go figure. Quote of his old review, and our comment at the bottom of this post.
Canon may slowly lose its edge, market share, brand luster etc, but there's one thing that hasn't changed, and is highly characteristic of the company: it doesn't leak. At least, not uncontrollably, as opposed to all of its major rivals who lately seem to have lost the ball. We've got raw files from Nikon's latest and 'bestest' circulating in the wild, all the while there's a supposed NDA in place to disallow just that, we found out almost everything about Olympus E-M5 before it was officially announced, and so on.
This article goes way beyond the dreaded 'error 99' that has plagues countless EOS shooters:
"EOS digital SLRs began by displaying a series of possible Error Codes, depending on the nature of a detected problem. In early years, these