. The Bell System technical journal . crometer scale was focused on the index markon the barrel of the projection lens. A lens displacement of inchcaused the index to traverse 50 divisions of the scale. External Aperture An adjustable black paper mask mounted 1| inches from the prin-cipal planes of the lens, on the screen side. The opening was rec-tangular, with sides horizontal and vertical, of constant area squareinch. The ratio of height to width could be varied continuously to without changing the area. The opening was uniformlyfilled with light under all conditions
. The Bell System technical journal . crometer scale was focused on the index markon the barrel of the projection lens. A lens displacement of inchcaused the index to traverse 50 divisions of the scale. External Aperture An adjustable black paper mask mounted 1| inches from the prin-cipal planes of the lens, on the screen side. The opening was rec-tangular, with sides horizontal and vertical, of constant area squareinch. The ratio of height to width could be varied continuously to without changing the area. The opening was uniformlyfilled with light under all conditions. Viewing Screen White Bristol board, inches high by inches wide (the imagesize of an available television receiver to be used for comparison).The screen was hung at the back of a black-velvet-lined box 18 incheshigh, 22 inches wide and 12 inches deep. The viewing distance wasalways 30 inches. The viewing room was completely darkened except for a little straylight from the projection machine. 584 BELL SYSTEM TECHNICAL JOURNAL. Scene 1 Scene 2
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
