Photography by Infra-Red

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Technical Note (National Research Council of Canada. Division of Building Research), 1955-10-19

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Photography by Infra-Red

Sereda, P. J.

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DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

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N 1I CAlL

NOT 'FOR PUBLICATION

NOTlE

No.

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FOR INTERNAL USE PREPARED BY P. J. Sereda CHECKED BY E. V. Gibbons APPROVED BY

R.F.L.

PREPARED FORDivision of Building Research

SUBJECT

PHOTOGRAPHY BY

INFRA-RED

During some work for the Associate Committee on Corrosion Research and Prevention the writer had occasion to tryout the photographic technique involving infra-red sensitive film. The following note summarizes what was learned during the course of this work for the benefit of others in the Division who may have occasion to use this method of recording data.

A very useful source of information on this subject is a book entitled i1Photography by Infra-redi l

by vial ter Clark, J obn Wiley

&

Sons,

1946.

Infra-red radiation which is just beyond the visible red end of the spectrum, and having a wavelength of 7,600

-5,000,000 A is produced by the sun, incandescent lamps and to a lesser degree by all objects at elevated temperatures.

The amount of any incident radiation that is absorbed and the amount reflected by an object is dependent upon the ｷ｡ｶ･ｬ･ｮｧｴｾ

of the radiation and the characteristics of the materials comprising the object. It is for this reason that objects will often appear different when photographed on infra-red sensitive film than when photographed on panchromatic film by visible light. It is this fact that enables certain observations to be made on materials which could not be seen under normal conditions. Changes in the

chemical composition of surfaces such as occur during the corrosion of the surface can often be detected by infra-red photography

before they are apparent to the naked eye.

Alth6ugh a variety of infra-red sensitive film is available only one, Kodak High Speed Infra-red Safety Film, was triedo It

was found that this film required more care than is normal with panchromatic film. First the ordinary metal cassette used vith

35

rom. panchromatic film 'lims _{not adequate and fogging occur-:r'sd aT;} the slit where film is unrolled. Therefore tLle film had to be

---·

.

loaded directly into the camera in total darkness and likewise unloaded for processing. The hard rubber developing tank was likewise somewhat transparent to infra-red and fogging occurred. A safellght specific for infra-red should be uned when processing .. The most serious fogging was encountered from the ｡ｦｴ･ｲｾｧｬｯｷ of incandescent lamps in the darkroom if the film was exposed soon after the lights were turned out. Thus a period of a few

minutes was required after lights were turned out to ensure dark conditions. It sh uld be remembered that many objects which are opaque to visible light are transparent to infra-red radiation. The film has the speed characteristics of super XX film and when ordinary exposure meters are used the

A.S.A.

_{speed rating appear3}

to be about

125

when using the Wratten A filter. Thus satisfactorj photographs can be made vJ"1th incandescent lights at camera setti .gs of

1/25

sec. and f8.

It was found that indirect lighting gave the highest contrast. Such lighting can be obtained by having the photo flood lights

shine on white non-glossy paper reflectors located just behind and to each side of the camera.

The film after exposure can be processed in a manner identical with that used for any other sensitive film and this is one of the

distinct advantages of the infra-red film over other special types of film. The negative thus obtained can be contact printed or enlarged in the normal manner.

The "frostyll scene depicted in the phot g aph shown below was taken from the window of our Chern. Labora on a sunny

day in September with the grass ｾｮ､ the trees green.