天文电子照相机

The Electrographic Camera for Astronomy

电子照相机是一种高效能的天文微光图像探测器。过去50多年以来,国外一些天文台曾付出了巨大的努力,成功地研制出几种不同结构型式的实用化整机,并将其同望远镜及摄谱仪配合使用,分别在地面和空间条件下,对天文光度学和天文光谱学领域中众多类型的研究课题,从事观测研究,取得了许多极有科学价值的研究结果。

The electrographic camera is one of the most powerful modern detectors in astronomy. The electro-graphic cameras of various types were produced in the past several decades, and many excellent astronomical results were obtained with these cameras for ground-based and space applications.In an electrographic camera, the primary photoelectrons are recorded directly on an electront sensitive photographic emulsion. The effectiveness in this manner is high, but it will lead to a. serious technological difficulty. The basis problem is that the electrron-senstitive emulsion must be placed in the same vacuum chamber as the photocathode, but both of them are incompatible-The photocathode is very active chemically and is poisoned instantaneously by gases and vapo (paticularly water-vapor) given off by the emusion.The experimental work on developing eletrographic cameras that we have been studying since. 1973, at Beijing Astronomical Observatory, is described in this paper, one of them is engaged in making an electromagnetically focused camera with an effective diameter of 100mm, that has had a preliminary result to be published. The other one is an electrostatically focused camera that has been brought to success now and tested on the 60cm reflector, at Xinglong Station, BeijinS Astronomical Observatory. The obtained limiting magnitude is about 17 on Kodak Ⅲa-J emulsion when 1-minute exposure under 20 kV is used, with no filter.Our electrostatically focused camera is similar to Kroa camera. It has been demonstrated that the camera has an effective field of view of 50mm in diameter, a resolution of better than 100Lp/ mm, a distortion of less than 2%, and an image magnification of 0.7. Its overall weight is about 40kg and the overall length is 54cm. The overall voltage is 20-30kV.Lastly, as a further studying step, we mention the importance for space astronomy to develop far-ultraviolet electrographic camera or its combination with the other detectors (for exampler with CCD or vidicon).