I guess those people must be real dumb to spend $30K on the digital back....(According to your explanation)
yeah, the psychology of someone buying a 30k equipment = it must be frickin best is kinda funny yet extremely common amongst humans alike.
digitals backs does not equate to a Canon Full-Frame.
no lens delivers light rays perpendicular to the surface of photosites, except at the optical center of the lens, which is usually in the center of the image. Perspective control lenses are the only ones that routinely change this arrangement. But every lens has its own focal length. Meaning that the angle of light rays from a telephoto lens and those from a wide angle lens are as different behind the lens as their angles of view are in front of the lens. In general, wide angle lenses paint their photons into the corners of images at a MUCH more acute angle than do tele lenses. So what? As light slams into photosites at an angle, they encounter several layers before banging into sensitized silicon. A clear "retarder plate" to confuse any residual polarization (don't ask), a clear, but mildly diffused "antialiasing" filter, a color filter, sometimes an anti-moire filter and an array of microlenses precede the sensitive patch of each photosite. Where all this becomes something of a problem is in its eventual real-world behavior at the photon level. The microlens atop the photosite is designed--in current technologies--to concentrate the totality of photons streaming into the whole area of the photosite onto its far narrower sensitive area in the center of the tiny photosite. It's a simple lens--a dome of refractive material designed to steer photons from the edges into the active center. Not seen in the artist's diagram above is the factoid that only about 10% of the photosite's area literally responds to light. Light arriving at an angle to the centered microlens isn't as efficiently steered into the photosite's sensitive center. Add to that the fact that wide angle lenses don't have corner coverage as bright as their optical center coverage--a different kind of optical phenomenon, but always a consideration in wide lens design--and a common result is that full-frame images increase corner vignetting with certain legacy wide angle designs. Film surfaces don't have these issues. Film is a flat, somewhat matte surface, every square micron of which is photosensitive.
Well, wasn't the Big Reason to make FF chips in the first place to be able to recycle all those previous purchases? Or was the Big Reason to give the previously all-film photographer the same depth of field he was enjoying in 1989?
With every solution comes its own problem.
Where all this meets the realm of practical reality is this: current FF camera owners are often--but not universally--aware of vignetting and softness issues in the corners of their images, particularly with wide angle, legacy optics.
Modern wide zoom designs targeting DSLRs can be--and often must be--designed around retrofocal optical principles, meaning that the rays streaming out their backs are not at the acute angles so often seen in legacy wide angle designs. And, as noted previously, new optic design principles, computational tools and manufacturing techniques are much more able to create superior lenses than those even a decade old.
Perhaps FF camera owners will be assuaged by knowing that the DOF from 1989 has been preserved.
Canon Full-Frames certainly isn't the "holy grail" of cameras but it does gives you bragging rights