electronographic camera

electronographic camera

(i-lek-tron-ŏ-graf -ik) A highly sensitive electronic device that can be used for recording astronomical images. It is an image tube in which the beam of electrons liberated from the photocathode is accelerated by an electric field and focused by a magnetic field on to a film coated with an electronographic emulsion. This is a very fine grain high-resolution ‘nuclear’ photographic emulsion in which electrons are recorded directly: every high-energy electron leaves a developable track so that an image can be produced by a process similar to that for a photograph. The resulting electronograph looks similar to a photograph with the important difference that the density at any point on the electronograph is proportional to the intensity at the corresponding point in the optical image through almost the whole intensity range. The device thus has a highly linear response. Photometric information can be obtained directly by measuring the density of the image. The device also has a high quantum efficiency.

Electronographic Camera

 

an electron-optical instrument for the reproduction of images of objects on an electrono-graphic plate that is sensitive to the action of a flow of electrons. In astronomy the electronographic camera is used in conjunction with telescopes of low relative aperture in such a way that the optical image of an object is projected onto the photocathode of the camera. The photoelectron flow that arises is projected by means of some electron-optical system (electrostatic, magnetic, electromagnetic, or combined system) onto an electronographic plate, where the electron image of the object corresponding to the optical image on the photocathode is fixed. The more efficient use of the luminous flux available (in comparison with conventional photography), especially in the infrared region of the spectrum, makes it possible to reduce photographic exposure times significantly and, in many cases, to increase the limiting magnitude of the telescope.

Since the density of an image on an emulsion is proportional to the density of the incident electron flow, and the latter thus depends on the illuminance on the photocathode, the characteristic curve of an electronographic camera does not exhibit the underexposure region that is typical of conventional photographic emulsions. This feature, together with the significant capacity of electronographic emulsions to register the total accumulated action of electrons over a period of time and the high resolution of such emulsions, makes it possible to use electronographic cameras to detect faint details of the spectra and structure of diffuse celestial objects.

The first astronomical electronographic camera was designed by A. Lallemand of France in the 1950’s.

REFERENCE

Kurs astrofiziki i zvezdnoi astronomii, 3rd ed., vol. 1. Edited by A. A. Mikhailov. Moscow, 1973.

N. P. ERPYLEV

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