infrared photography

(redirected from Infra-red photography)
Also found in: Dictionary.

infrared photography

[¦in·frə¦red fə′täg·rə·fē]
(graphic arts)
Photography in which an infrared optical system projects an image directly on infrared film, to provide a record of point-to-point variations in temperature of a scene.

Infrared Photography

 

(also IR photography), the production of photographs using infrared radiation. Photographs can be taken in IR radiation in several ways. The simplest method is that of direct photography, using photographic plates or film that are sensitive to IR radiation. In this case a light filter that passes IR radiation but is opaque to visible light is mounted on the camera lens. Modern materials for infrared photography have a sensitivity threshold in the long-wave region of λ = 1.2 microns (μ).

The sensitivity of infrared film and plates is relatively low; therefore, at low illumination intensities apparatus consisting of an image converter and a standard photographic camera is used for infrared photography. The image converter, which is placed in front of the camera lens, converts the invisible infrared image into a visible image, simultaneously increasing its brightness. Such apparatus makes possible the production of photographs on standard film in complete darkness and with a low-powered IR radiation source. The sensitivity threshold in the long-wave region is dependent on the photocathode of the image converter and does not exceed λ = 1.2 λ.

Special apparatus makes possible the production of infrared photographs in the region where λ > 1.2 η. One such device, the infrared vidicon, is a television system in which the screen of the camera tube is made of photoconductive semiconductor materials, which change their electrical conductivity under the influence of infrared radiation. A visible television image appearing on the screen of the picture tube is then photographed by a standard camera. The long-wave limitations of the vidicon depend on the nature of the material of the photoconductive screen and on its temperature; at T = 79°K (with liquid nitrogen cooling) the limit is λ ≈ 5 μ; at T = 21°K (with liquid hydrogen cooling), λ ≈ 20 μ.

Infrared photography makes it possible to obtain additional data about an object (as compared to photography in visible light or visual observation). When passing through haze or fog, infrared radiation is dispersed to a lesser degree than visible radiation, making possible the production of sharp photographs of remote objects over distances of hundreds of kilometers. Because of the difference in reflection and transmission coefficients between the visible range and the infrared range, infrared photographs show details invisible to the eye on standard photographs. These particular features of infrared photography are widely used in botany for studies of plant diseases, in medicine during diagnosis of skin and vascular diseases, in criminology for detection of forgeries, in infrared aerial surveying, and in astronomy for photographing stars and nebulas. Infrared photographs can be taken in complete darkness.

Devices are also made that are capable of recording thermal IR radiation by an object whose temperature is different at different points. The intensity of IR radiation at each point is recorded by the receiver and is converted into a light signal, which is in turn recorded on photographic film. The image produced in this case is not an infrared photograph in the usual sense, since it depicts only the temperature distribution on the surface of the object. Such devices are used in detecting overheated areas of machines and in infrared aerial surveying to produce a thermal map of a locality.

REFERENCE

Clark, W. Photography by Infrared, 2nd ed. New York, 1946.

V. I. MALYSHEV

infrared photography

Photography employing an optical system and direct image recording on film sensitive to near-infrared wavelength (infrared film). This should not be confused with infrared imagery. The term infrared photography is misleading, in that the infrared portion of the spectrum extends approximately from 0.7 to 300 microns in wavelength. Infrared photography, on the other hand, normally includes wavelengths no greater than 1 micron. The recording of near infrared (i.e., at wavelengths between 0.7 and 1.5 microns) does not differ significantly from the recording of visible radiation and is called near infrared to distinguish it from imagery obtained with longer wavelengths of infrared energy.
References in periodicals archive ?
An old technique with improved applicability to rock art research is infra-red photography or, in its modern incarnation, digital infra-red imaging.
Infra-red photography in archaeology and conservation
Infra-red photography captures the red end of the colour spectrum beyond standard colour and black and white film.
Infra-red photography has long been employed in the fields of art history and conservation to detect under-painting and sketch lines that are largely obscured by over-painting and varnish (Bridgman & Gibson 1963; Gibson 1978: 144-8).
The need to keep infra-red film cool and process it soon after exposure makes infra-red photography difficult in many field situations.
But it would take time-lapse, infra-red photography to catch the culprit.