pinhole camera

Definition: Design of camera in which a small hole replaces the lens. * Such a camera offers a wide-angle field, is free of distortion and does not require focusing but field curvature and chromatic aberrations are a problem. * The hole must be very cleanly cut e.g. with a laser: the focal length of the camera is the distance from the hole to the film. * The optimum diameter of the hole may be calculated: one guide is that the diameter of the hole equals the square root of the focal length multiplied by 0.035. Bet you never thought of this As pinholes bend any radiation it follows they can be used to record any radiation. That's right, you can use pinhole cameras to record ultra-violet or infra-red ... even x-rays (if your pin-hole is in a solid lead plate). All you need in the box is a suitably sensitised film. Which, incidentally, you can place curved, so as to compensate, at least a bit, for the field curvature.

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