The Faint Object Spectrograph (FOS) was a spectrograph installed on the Hubble Space Telescope . It was replaced by the Space Telescope Imaging Spectrograph in 1997, and is now on display in the National Air and Space Museum in Washington DC.
6-604: A technical description of the construction and operation of the FOS can be found in NASA technical report CP-2244. The instrument used two digicon detectors, 'blue' and 'red', and had a spectral resolution of about 1300 over the 115 nm to 850 nm range. It had a number of apertures of varying size, but the aberration of the HST mirror meant that, until COSTAR was installed, the smallest apertures suffered very serious loss of light; even
12-467: A vacuum to focus the electrons released from a photocathode by incoming light onto a collection of silicon diodes . It is a photon-counting instrument, so most useful for weak sources. One of digicon's advantages is its very large dynamic range and it results from the short response and decay times of silicon diodes. In 1971, E.A. Beaver and Carl McIlwain successfully demonstrated a way in which silicon diodes can be used in digital tube by placing
18-628: A silicon diode array that contained 38 elements in the same chamber as a photocathode. The design and manufacture of the Digicon tube is attributed to John Choisser of the Electronic Vision Corporation. Digicon detectors were used on the original instruments for the Hubble Space Telescope , but are very rarely used in new designs, where CMOS active-pixel detectors can achieve the same performance without
24-401: The largest 4.3-arcsecond aperture collected only 70% of the light from a point source. The digicons suffered from inadequate magnetic shielding, which meant that a static image was smeared over several pixels; the red digicon suffered most from this. Also, either the blue detector or one of the mirrors in the system was contaminated in such a way as to remove sensitivity below 150 nm; this
30-624: The need for large electric fields or complicated vacuum assemblies. For instance, there were two pulse-counting Digicon detectors in the Goddard High Resolution Spectrograph installed on the Hubble Space Telescope from 1990–1997, used to record ultraviolet spectra. Digicon is also used in digital imaging such as the case of a scanning gage using Digicon imaging tube, which generates a two-dimensional view with high spatial resolution when an object
36-472: Was a serious problem since it makes the Lyman-alpha line at 121.6 nm inaccessible. This article about a specific observatory, telescope or astronomical instrument is a stub . You can help Misplaced Pages by expanding it . Digicon A digicon detector is a spatially resolved light detector using the photoelectric effect directly. It uses magnetic and electric fields operating in
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