A monoscope was a special form of
video camera tube which displayed a single still video image. The image was built into the tube, hence the name. The tube resembled a small
cathode ray tube (CRT). Monoscopes were used beginning in the 1950s to generate TV
test patterns and station logos. This type of test card generation system was
technologically obsolete by the 1980s.
Design
The monoscope was similar in construction to a
CRT
CRT or Crt may refer to:
Science, technology, and mathematics Medicine and biology
* Calreticulin, a protein
*Capillary refill time, for blood to refill capillaries
*Cardiac resynchronization therapy and CRT defibrillator (CRT-D)
* Catheter-re ...
, with an electron gun at one end and at the other, a metal target screen with an image formed on it. This was in the position where a CRT would have its
phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...
-coated display screen. As the
electron beam scanned the target, varying numbers of electrons were reflected from the different areas of the image. The reflected electrons were picked up by an internal electrode ring, producing a varying electrical signal which was amplified to become the
video
Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...
output of the tube.
This signal reproduced an accurate still image of the target, so the monoscope was used to produce still images such as test patterns and station logo cards. For example, the classic
Indian Head test card as used by many television stations in North America, was often produced using a monoscope.
Usage
Monoscopes were available with a wide variety of standard patterns and messages, and could be ordered with a custom image such as a station logo. Monoscope "cameras" were widely used to produce test cards, station logos, special signals for test purposes and standard announcements like "''Please stand by''" and "''normal service will be resumed''....". They had many advantages over using a live camera pointed at a card; an expensive camera was not tied up, they were always ready, and were never misframed or out of focus. Indeed, monoscopes were often used to calibrate the live cameras, by comparing the monoscope image and the live camera image of the same test pattern.
Pointing an electronic camera at the same stationary monochrome caption for a long period of time could result in the image becoming
burnt onto the camera tube's target — and even onto the
phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...
of a monitor displaying it in extreme cases.
Monoscopes were used as
character generators for
text mode video rendering in
computer displays for a short time in the 1960s.
The monoscope declined in popularity after the 1960s due to its inability to generate a colour
test card, and the development of
solid state
Solid state, or solid matter, is one of the four fundamental states of matter.
Solid state may also refer to:
Electronics
* Solid-state electronics, circuits built of solid materials
* Solid state ionics, study of ionic conductors and their u ...
TV test pattern signal generators.
See also
*
Test card, the updated, coloured version of monoscopes.
References
External links
Monoscope tubes* The Museum of the Broadcast TV Camera, picture and description of th
(UK)
* Picture and description of th
(US)
Indian Head - "as transmitted" picture2F21 data sheet
{{Electronic components
Display technology
Television technology
Test cards
Vacuum tubes