(under subclass 443) Subject matter including a lens combined with the screen, the screen usually being positioned in the second principle focal plane of the lens.
(1) Note. The device, commonly known as a camera obscura, usually has a darkened chamber with a lens at the entrance thereof to permit light from external objects to enter and to form an image of the objects on a screen in the chamber.
(2) Note. The combinations classified here are often constructed to function normally only when the light rays approaching the entrant lens from the object are substantially parallel, under which conditions the image produced by the device is always greatly reduced relative to the size of the object. The lens and screen combinations
classified in Class 353, Optics: Image Projectors, differ from those classified here in that they are constructed to operate normally only when the light rays approaching the entrant lens from the object are of the widely diverging type, that is, when the object is near the first principal focal plane of the entrant lens, under which conditions the image produced by the device is enlarged relative to the size of the object, a condition that usually necessitates the use of intense artifical object illumination to provide an adequately illuminated image. Moreover, the lens and screen combinations of Class 353, Optics: Image Projectors, always have their object and screen in the conjugate focal planes of the projection lens employed with the screen spaced more distant from the lens than the object, while the lens and screen combinations of this subclass 448 have their object and screen substantially at infinity and at the principal focal plane of the lens respectively.
SEE OR SEARCH THIS CLASS, SUBCLASS:
369, and 400, for a compound lens system combined with a viewing screen.
SEE OR SEARCH CLASS
353, Optics: Image Projectors, 18, 47, 67, 72+, 74+, and 79+ for an image projector having a light source or means to concentrate solar light and including a lens and screen combination. See (2) Note above.
