Vidicon
A Vidicon (German also Vidikon) is an image recording tube ( English video camera tube , not to be confused with the picture tube for reproducing a ( television ) picture) developed by the company RCA around 1950 . Even today, electron tubes of the vidicon type are still used for special tasks such as in highly radiant environments ( nuclear power plants ).
History and comparison to other image sensors
Compared to other image pick-up tubes (such as the orthicon or iconoscope ) that work with photocathodes and a fast electric scanning beam, the vidicon works with a photosensitive layer that is scanned with a slow electron beam. When it was first introduced, the Vidicon was smaller, lighter and more economical in terms of energy consumption, and it quickly established itself first in portable cameras. While the first Vidicons at RCA worked with selenium as the photosensitive layer, due to shelf life problems they quickly switched to antimony trisulfide. Vidicon type tubes with semiconductor layers other than antimony trisulfide are traded under different names (see table).
| Surname | Photo layer | Sensitive friendliness in mA / lm |
first manufacturer |
Word mark or production since |
disadvantage |
|---|---|---|---|---|---|
| Vidicon (Se) | Selenium (Se) | - | RCA | 1950 | maximum 40 ° C |
| Vidicon | Antimony (III) sulfide (Sb 2 S 3 ) | - | RCA | 1951 |
Dark current drag |
| Resistron | Antimony (III) sulfide (Sb 2 S 3 ) | - | PTW | 1954 | Dark current drag |
| Endicon | Antimony (III) sulfide (Sb 2 S 3 ) | - | WF | 1956 | Dark current drag |
| Plumbicon | Lead (II) oxide (PbO) | 0.4 | Philips | 1962 | Flare effects when overexposed |
| Leddicon | Lead (II) oxide (PbO) | 0.4 | EEV | 1975 | Flare effects when overexposed |
| Si multidiode vidicon |
Silicon diodes (Si) | 0.9 | several | 1972 | Flare effects with overexposure to dark current spots |
| Chalnicon | Cadmium Selenide (CdSe) | 1.5 | Toshiba | 1972 | Torch effects in overexposure retightening |
| Pasecon | Cadmium Selenide (CdSe) | 1.5 | PTW | 1976 | Torch effects in overexposure retightening |
| Saticon | Selenium Arsenic - Tellurium (SeAsTe) | 0.35 | Hitachi | 1973 | Flare effects when overexposed to a maximum of 50 ° C |
| Newvicon |
Zinc selenide - cadmium zinc telluride (ZnSe - Cd (x-1) Zn x Te) |
1.2 | Matsushita | 1974 | Flare effects with overexposure to dark current |
At the 1953 Düsseldorf radio exhibition in Germany, the manufacturer Grundig presented a Vidicon television camera, which was sensationally small and handy for the time and weighed only three kilograms, under the name Grundig-Fernauge .
The space probes of the American Mariner and Viking program used the Vidicon for their recordings, Mariner 4 used it to take the first close-ups of Mars . The space probes of the Voyager program also used Vidicon cameras for their recordings.
functionality
The light-sensitive layer consists of semiconducting materials such as selenium , arsenic , tellurium , or antimony (III) sulfide (Sb 2 S 3 ). It is applied to a pane of glass that is located on the front wall of the electron tube. A transparent, electrically conductive layer, for example made of indium tin oxide, ensures electrical contact . This signal plate is negatively charged by an electron beam . The image to be recorded changes the electrical resistance point by point due to the different local brightness , so that the charges migrate to the positive signal plate at different speeds. A charge image is created there, which is read out and deleted again with each new scanning process.
The electron beam is generated with a beam system like in a cathode ray tube . The cathode is indirectly heated electrically and consists of suitable materials in order to be able to release electrons at a low temperature. The electron gun is usually designed as a triode: the positive field of the acceleration grid "grabs" through the hole in the negatively charged Wehnelt cylinder and sucks the electrons out of a "virtual" cathode from an electron-optical point of view (the virtual cathode is actually a cloud of electrons above the cathode). The cathode current is controlled with the voltage of the Wehnelt electrode. A so-called “crossover” point is formed near the Wehnelt cylinder, which is imaged onto the photosensitive layer with a focusing coil around the tube. The magnetic beam deflection system consists of saddle coils similar to those used in picture tubes . The deflection creates a focus error in the beam that has to be corrected. A net in front of the photosensitive layer ensures that the beam is not deflected by the charged layer.
Further developments
In 1962, Philips developed the Plumbicon , which uses lead oxide (PbO). The advantages of the Plumbicon are the compact design, the simple mode of operation and the possibility of following a quick image change with almost no inertia, which is why this tube was used almost exclusively in television operations and replaced other types.
Color images
Color images were made possible by using three tubes in one camera. The incident light is split into three tubes with a beam splitter . Before each tube one ever sits RGB - color filters of red, green and blue, so that each video tube only the corresponding color components of the image colors are recorded that are then reassembled in the later display on the TV.
This structure was too complex for the consumer sector, so cameras with strip filters were developed. In addition to a low resolution (typically 220 columns horizontally), images recorded in this way showed strong moiré effects .
As a result of the further development of color filter technology, mosaic filters are used today that reduce the moiré effect, but cannot prevent it.
Size specification
A peculiarity of the size of the video tube still determines the size of the sensors of digital cameras today : In the past, the outer glass diameter of the light-sensitive front surface was given in inches . The real usable screen diagonal was about 2/3 of it. For example, the classic 1-inch Vidicon XQ-1030 with an aspect ratio of 4: 3 has a usable image area of around 10 mm × 13 mm, which corresponds to a diagonal of 16.4 mm. Although 1 "(1") is 25.4 mm, a tube is called a 1 "tube and has an effective screen size of 16.4 mm. This strange calculation is still used today. A modern 1 / 2.7-inch sensor therefore only has a real image diagonal of 1 / 2.7 * 16.4 mm = 6.07 mm and not 9.41 mm. The size differences vary slightly depending on the type of sensor and the aspect ratio.
The calculation based on 16.4 mm ≘ 1 ″ can only serve as a guide, since the ratio of tube diameter to screen diagonal is not a constant.
See also
literature
- A. Rose: Photoconductivity in insulators. In: RCA Rev. 12, 1951, pp. 303-305.
- PK Weimer, SV Forgue, RR Goodrich: The Vidicon — photoconductive camera tube. In: RCA Rev. 12, 1951, pp. 306-313.
- PK Weimer, AD Cope: Photoconductivity in amorphous selenium. In: RCA Rev. 12, 1951, pp. 314-334.
- SV Forgue, RR Goodrich, AD Cope: Properties of some photoconductors, principally antimony trisulfide. In: RCA Rev. 12, 1951, pp. 335-349.
- RW Smith: Some aspects of the photoconductivity of cadmium sulfide. In: RCA Rev. 12, 1951, pp. 350-361.
- A. Rose: An outline of some photoconductive processes. In: RCA Rev. 12, 1951, pp. 362-414.
- RM Schaffert, CD Oughton: Xerography: a new principle of photography and graphic reproduction. In: J. Opt. Soc. Amer. 38, 1948, pp. 991-998.
- RH Bube: Photoconductivity of solids. Wiley, New York 1960.
- A. Rose: Concepts in photoconductivity and allied problems. Wiley, New York 1963, OCLC 536272 .
Web links
- Specialty Tubes - Lots of excellent photos from video tubes
- Common Image Sensor Sizes
- Video scanning tubes
- The 1953 Vidicon
Individual evidence
- ↑ a b c d e f g h i j B. Heimann, W. Heimann: TV camera tubes - properties and applications. In: TV and cinema technology. 32 (9/10), 1978, pp. 1-13. (PDF)
- ↑ DPMAregister: Marke 661761 (accessed on June 26, 2016)
- ↑ DPMAregister: Trademark DD614938 (accessed on June 26, 2016)
- ↑ DPMAregister: Marke 945940 (accessed on June 26, 2016)
- ↑ Alexander Mayer: Grundig and the economic miracle. Working worlds series, Erfurt 2008, ISBN 978-3-86680-305-3 , p. 47.
- ↑ Funk-Technik No. 24/1953.
- ↑ NASA : Mars TV-Camera (Mariner 4); NASA: Orbiter Imaging (Viking).
- ↑ Cameras in Voyager probes [1]