Electronic camera

Introduction

Chinese and English name

[Chinese entry]Electronic camera

[Foreign entry]electronographic camera

An electric vacuum imaging device that replaces the phosphor screen in the image tube with a fine-grained film.

Application field

Astronomical system application

The photoelectric imaging system attached to the astronomical telescope. It is mainly composed of a photocathode, an electron lens and a negative film installed in the shell of the high vacuum tube. The photocathode turns the optical image reflected on it into an electronic image, which is focused and accelerated by an electronic lens system, and recorded on a negative film sensitive to electrons impacting at high speed. The photographic density of the electronic image on the film has a linear response relationship with the incident light intensity in a wide range. The information storage capacity and dynamic response range of electronic photos are large, the gray fog and dark background are small, and the resolution is as high as 200 line pairs per millimeter or more. In addition, a single electron emitted from the photocathode is accelerated to more than 25 kV, which can produce a recognizable electron trail on the film, thus reaching the theoretical limit of a radiation detector. The electronic camera can record accurate images of all celestial bodies in the entire field of view at the same time with high efficiency, which is very suitable for photometry and spectrophotometric measurement of dim celestial bodies. For example, it can accurately determine the magnitude of celestial bodies on uneven backgrounds, observe dense galaxies, diffuse nebulae, and faint celestial bodies such as quasar radio sources, take high-dispersion spectra, and increase the detection limit of telescopes. In addition, electronic cameras have also been successfully used in space astronomy.

Technical shortcomings

In a high vacuum, the film latex will release water vapor and other gases, which will cause the photocathode, which is very chemically active, to be damaged in an instant. To avoid this phenomenon, many complicated technical problems need to be solved. At the same time, there are also some difficulties in the use of electronic cameras.

Structural description

Kronan structure. Electrodes 2, 3, 4 of the electronic lens are arranged in the metal tube shell, and the electrodes are separated by a glass tube shell. The photocathode 1 is prepared on a sapphire substrate and forms a set of image field correction system with two front optical lenses. There is a high vacuum valve 5 between the film box 6 and the photocathode. When the film box is removed and replaced, it can be closed to protect the photocathode. 7 is the valve operating mechanism, and 8 is the magnetic shield sleeve. The negative film is installed on a circular film carrier, and the latter rotates under the action of an external magnet to sequentially expose each negative film to the electronic image. The film cassette is cooled with liquid nitrogen.