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I know who Jim Frazier is and what he has done, but I only have basic knowledge of his invention. Could someone please explain what he has done further?
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The detailed explanation is available in the patent (US5727236), which is available at Google Patents, among other places.
A simplified explanation is that he developed a system that uses two lenses. The primary lens is a very wide-angle lens, and like all wide-angle lenses, it has a very large depth of field for any given aperture (and the aperture is kept fairly large in Frazier's design). That's what gives the deep-focus "magic"; a very wide-angle lens. There's nothing too very special or revolutionary about that.
This particular wide-angle lens, though, also throws a wide image circle. In other words, it makes a very big picture for its focal length. Again, nothing spectacular there; covering a large film frame with a short focal length lens is something optical designers have been doing for quite some time.
The image that the wide-angle lens throws isn't used directly by the camera, though. It's focused on a pellicle element (which takes the normal place of film or a sensor) and viewed through a separate lens behind the wide-angle lens. This second lens can zoom in on the projected wide-angle image, giving an apparently longer focal length and allowing the aperture to be varied as necessary for photography/filming exposure while maintaining essentially the "baked-in" depth of field of the primary wide-angle lens. By itself, that has also been done before, as explained in the "prior art" section of the patent.
There is also a system of prisms in the system that allows the lens to be aimed without altering the camera's orientation. That part of the system is not too very different from an adjustable periscope. Again, that's not novel in itself.
It's the entire system taken together — using a large image circle from a very wide angle lens at an optimal wide aperture for that lens, taking a picture of that lens's picture through a separate lens, and having a system for articulating and orienting the two-lens system — that was patentable and award-winning. (However, it seems he blew the patent protection, at least in some jurisdictions, by poor choice of promotional methods. See the Wikipedia article for more details and links.)