APPL-1013 / Page 1 of 3
`APPLE INC. v. COREPHOTONICS LTD.
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`

`

`Library of Congress Catalog ing- in-Publication Data
`
`the International Socie ty fo r Optical
`
`Kingslake, Rudolf.
`Optics in photography / Rudolf Kingslake.
`cm.
`p.
`"A Publication of SPIE-
`Engineering ."
`Includes bibliographical references and index.
`ISBN 0-8 194-0763- 1
`1. Photographic optics.
`TR220.K56 1992
`77 l.3'5--dc20
`
`I. Title.
`
`92-1186 1
`C IP
`
`Published by SPIE- The Internation al Society for Optical Engineering
`P.O. Box 10
`Bellingh am, W ashington 98227-0010
`
`Design: Matt Treat
`Composition: Carrie Binschus
`
`Copyright © 1992 The Society of Photo-Optical Instrumentation Engineers
`
`All rights reserved. No part of this publication may be reproduced or distributed
`in any form or by any means without written permission of the publisher.
`
`10 9 8 7 6 5 4 3 2 1
`
`Printed in the United States of America
`
`APPL-1013 / Page 2 of 3
`APPLE INC. v. COREPHOTONICS LTD.
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`

`

`Chapter 6
`
`The Brightness of Images
`
`T he relation between the aperture of a lens and the brightness of the image
`prod uced by it on the photograph ic emulsion is often misunderstood, yet
`it is of the greatest importance to the photographer who wishes to make the
`best use of the equipment. The tremendous efforts of lens designers and
`manufacturers tha,t have been devoted to the production of lenses of
`extremely h igh relative aperture are an indication of the need that exists
`for brighter images and "faster" lenses.
`In this chapter, we are concerned with the flow oflight from an object,
`through a lens, to the image. Several photometric terms must be under(cid:173)
`stood before we can give a precise statement of th is effect, and of the factors
`that con trol the brigh tness of the image projected on the film in a camera.
`The illumination (illuminance) produced by a lamp at any distance
`from it is found by div iding the candle power of the lamp by the square of
`the distance ( the inverse square law ). Thus, a SO-candle lamp will produce,
`at a distance of 3 feet, an illumination of 50/9 = 5.6 foot-cand les. The
`illumination in a we ll-lighted factory or classroom may reach 50 foot(cid:173)
`candles, and in motion-picture or television studios, illuminations as high
`as 200 to 300 foot-cand les are common.
`The term flux is used to express a quantity of light. The unit of flux is the
`lumen, defined as the amount of light falling on each square foot of a surface
`under an illumination of 1 foot-candle; hence, foot-candles and lumens per
`square foot are two ways of expressing the same thing. The convenience of this
`term may be seen by an example. Suppose we know that a certain 16mm
`projector emits 550 lumens. Then, if the projected image is3 x 4 ft, the average
`illumination on the screen will be 550/12 = 46 foot-candles; if the image is 5
`x 6.6 ft, the illumination will be 550/(5 x 6.6) = 16.7 foot-cand les, and so on.
`
`104
`
`THE BRIGHTNESS OF !MAGI
`
`The brightness (lumin
`power per unit area. Thus,
`lamp has about 2500 candh
`is thus about 25 candles pe1
`brightness, but it is excee
`projection, which sometir
`millimeter, and by the sur1
`2000 candles per square m
`At the other end of tr
`under ordinary room light
`calculating the brightness
`
`where k is the reflectivity
`illumination in foot-cand l,
`the illumination in the roe
`brightness of white paper\\.
`This is equal to 14/930 = C
`are 930 square millimeters
`The formula ( 6.1) cot
`surface is not always appli
`sandblasted metal, metall i,
`tends to reflect light some
`equal to the angle of incid,
`brighter than white paper
`duller than white paper in
`in this chapter (page 135)
`The inconvenience of(cid:173)
`new brightness unit has bee
`to 1/rt = 0.32 candles per s
`required to express the brig]
`of candles per square foot. Ir
`
`We conclude, therefo1
`reflective and perfectly diffw
`candles falling upon it.
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`APPL-1013 / Page 3 of 3
`APPLE INC. v. COREPHOTONICS LTD.
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