ISO INTERNATIONAL STANDARD 9358 First edition 1994-07-15 Optics and optical instruments Veiling glare of image-forming systems - Definitions and methods of measurement Optique et instruments d'optique -- Lumiere parasite diffuse des systemes d'imagerie --- Definitions et methodes de mesure tso Reference number ISO 9358:1994(E) Copyrightltematinal Organizatin for Standardization No reproduction or networking permitted without license from IHS Not for Resale ISO9358:1994(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (isO member bodies). The work of preparing International Standards is normally carried out through Iso technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with IsO,also take part in the work.Iso collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated tothe memberbodies forvoting.Publication as an International Standard requires approval by at least 75 % of the member bodies casting avote. ISO/TC172,Opticsandoptical instruments,SubcommitteeSC1,Funda- mental standards. ISO1994 All rights reserved.Unless otherwise specified,nopart ofthis publication may be reproduced microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56 · CH-1211 Geneve 20 · Switzerland Printed in Switzerland CopyrightInternational Organization for Standardization No reproduction or networking permitted without license from IHS Not for Resale o ISO ISO9358:1994(E) Introduction The image plane of an optical or electrooptical imaging system normally receives not only the image forming radiation, but also stray (unwanted) radiation which can reduce image contrast. This unwanted radiation is referred to as "veiling glare". In lens systems it usually arises from one or more of the following causes: a) internal multiple reflections between the lens surfaces; (q scatter from the surfaces of the lens elements due to scratches and other imperfections in the polish, dirt and dust, fingerprints, grease, c) bulk scatter from the interior of the glass and from bubbles and striae; d) scatter from optical cements; scatter and reflections from ground edges of the lens elements, from internal lens mounts and from the internal surfaces of the lens barrel; f) reflections from the surfaces of diaphragms and shutter blades; g) fluorescence of the glass optical cements. The veiling glare of lens on its own can be considerably different from the veiling glare of a lens system and camera body combination. In the latter case, reflection of part of the image-forming radiation from the from the lens system and camera body contribute significantly to the veilingglare. In electrooptical devices, veiling glare arises from similar causes. For in- stance, in an image intensifier tube glare can arise from: a reflected by internal structures back onto the photocathode; b) radiation emitted from the phosphor going back to the photocathode; c) in tubes with microchannel plates some electrons incident on the input face can be back-scattered from this face before returning to it with the primary electrons. For the purposes of this International Standard, it is important to differen- tiate between veiling glare which originates from radiation incident on the entrance pupil or input face of an optical or electrooptical system and other factors which may cause a reduction in contrast and which may therefore influence a measurement of veiling glare. ili cense from IH Not for Resale