All, I think we've been over this before, but it's coming up again with the impending release of the *ist-D, I guess. I've got two points to make:
First, the angle at which light hits the focal plane is more important for a CCD array than for film. Why? The microlens array in front of the CCD! The light-gathering area of a CCD is only a fraction of the chip surface area. Sony (and others) maximize the light gathering capability of the CCD by putting an array of tiny lenses in front of the CCD. Take a look at this image from Sony's website: http://www.sony.net/Products/SC-HP/SG/CCD/superhad.html It should be fairly clear from the figure at the bottom that light striking the CCD perpendicular to the array gets focused on the sensor. What is not shown is that light striking at an oblique angle will get focused adjacent to the sensor, not on it. Second, the key is not to make the light purely perpendicular, but rather to minimize the angle. Yes, lens designers can affect through different lens designs. Consider retrofocus wide-angle lenses. A "simple" 15mm lens would have to be about 15mm from the image plane to focus at infinity. That would be far inside the mirror box of a 35mm SLR. For such a lens, least some of the light rays striking the image plane near the corners would be steeply angled. Retrofocus designs put the rear lens element out of the 35mm SLR mirror box, and coincidentally limit the angle at which light rays can strike the film plane. Hope this clears things up a bit, Mark
