Image Orthicon is a photoemissive type of camera tube. Photoemission is the basis of its working. This camera tube was invented in the year by Radio Corporation of America. Photocathode acts as a primary element in the operation of image orthicon. This is so because photocathode allows the emission of electrons from its surface when light from a scene is allowed to incident on it.
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It affected me immediately. There was a stronger contrast too that seemed to amplify everything and give more impact. Some episodes though, were produced with electronic cameras incorporating an Image Orthicon tube.
The electrical signals from the cameras are recorded on magnetic tape, rather than film strips, and this was done to save money when production budgets were tight. After I watched that episode I did some research to find what made it look different.
That was years ago and the whole thing just stayed in the back of my mind, but recently the interest grew again and some Internet searching brought me to someone who has a passion for this stuff. His name is Richard Diehl, a. A As a very young child, around age four, I was absolutely fascinated by our "big" black and white television. My memory says 23 inch, reality was probably 15 inch. I would put my nose to the screen and see the scan lines.
It actually made me angry that the image wasn't completely flat and homogeneous! It became imperative that I figure out how that worked. Once in school, I discovered books on the subject. But, the age appropriate material was too short on detail.
When in the second grade, Dad was stationed in Munich Germany, being in the Army, and we had to have our small Emerson 11 inch set readjusted to receive sound in Europe.
The fellow came to the house. Using my mother to translate, I grilled that poor guy on what he was doing. He patiently explained audio sub-carrier to me, through mom, and the best part was I understood what he was talking about. I had just learned how radio stations worked on the dial! It made complete sense!
Also, at that same time, I already knew what the image orthicon was! The Ernie Kovacs show would come on and his character, Percy Dovetonsils, would say "Greetings over your orthicon tube.
I pestered my folks as to what that meant until they researched the question and told me it "was" the TV camera. Everyone who met that little brat back then also learned about the magical orthicon tube! We had no word for OCD or evil medications then. Thank goodness! In my teen years, people started giving me old dead televisions and radios.
I was fixing the radios at age 11 and my first TV at that time. One day Dad came home from a yard sale. He had a rather large black book in his hand for which he paid no more than a quarter. He said, "I found this book and I think it's going to give you a religious experience! It was, sort of. It started me down the road to video. Ham radio slow scan TV was the big thing in the late 60s.
One of the ham radio magazines had a construction article for an SSTV monitor. I built that at around age Next came a copy of a vacuum tube camera by Dage.
The source of video junk in those times was a surplus store called Denson Electronics, in Rockville Connecticut. Al Denson and I exchanged letters on the topic and he provided a schematic and some of the critical parts to construct the camera.
It worked! Sort of. I rebuilt this camera into a full transistor job when an article appeared in Radio Electronics magazine. I was able to get pictures from it after a fashion. But, there was a typo in the schematic that I was not made aware of at the time. But, it counted! Then, I joined the Air Force in and things took off. I bought a reel to reel video tape recorder and camera outfit and was in like Flynn! TV cameras, fax machines, printers, scanners, computer graphics, etc.
My favorite imager is the Image Dissector tube by Farnsworth. Poor guy. His tube is perfect for every type of imaging The faster you scan a dissector, the less sensitive it is. How ironic. The tube lacked an important property called charge storage. Zworykin at RCA had a tube with this property, but loaded with other problems of its own, particularly related to scan geometry.
Its photosensitive surface, the mosaic, was too thick to be scanned from the back side, and had to be scanned from the front. The electron gun was typically oriented at around 45 degrees aiming "up" at the mosaic.
This resulted in a scan resembling the stroke of a windshield wiper. It was key stoned and required scan correction on the fly. In vacuum tube circuits, the last thing you want is more tubes! Cost, heat and power consumption shoot through the roof! A The "orth" in the name orthicon refers to the linear sensitivity of the photosensitive materials used. From the Greek "orthos" that means just that: straight or erect. Albert Rose and Richard Webb carried the terminology forward in the image orthicon.
No single person "invented" television. Q The Orthicon tube is known for the dark halo effect but I noticed two other effects as well: lifelike smoothness of motion and geometric distortion.
Let's start with smoothness. Is that due to faster rate of frame or the electronic scanning versus the advancing of still images with film? A Eventually, Albert Rose and a team at RCA took all the best attributes of the dissector and iconoscope and combined them.
The orthicon tube was born. It had plenty of problems and each solution made it just that much more complex. It had a backside scanned mosaic and weird hybrid scanning. The vertical was electrostatic, the horizontal magnetic. This tube never passed the experimental phase. Finally, they added the "imager" portion of the dissector tube to the front of the orthicon and made the hybrid image orthicon tube. The imager section has the same photo surface and electron lens arrangement as the dissector tube.
The difference is at the back. The pin hole aperture is replaced with a charge storage surface. The electron image is cast onto the thinnest piece of soda glass known up to that time.
It was made by blowing a bubble of glass, thickness measured optically with structured light sodium vapor lamps as lasers were a few years off. When the thickness was correct, a beryllium ring was pressed into the bubble and the excess glass was cut away.
The electron image lands on this glass called the target. It is so thin, the electron charge can be read from the back side of the glass. High velocity light induced electrons deplete the charge on the glass by knocking out electrons. The scanning beam puts them back on each scan. The reflection of the scanning beam, what I think of as a "spray" - think water hose blasting a wall, is picked up at the back of the tube and amplified. The missing charge in this return beam IS the video signal!
As for the image smoothness artifact, it is caused by the lack of charge storage between scans, known as lag. Also, there is some spreading of the charge that evens out noise, giving the smooth appearance to large flat areas of constant brightness.
The target is biased right to the hairy edge of balance. Just enough beam to erase the entire last image and no more. More beam ends up knocking out secondary electrons and surrounding bright spots with incorrect charge - dark halos in the output signal.
Unlike the vidicon tube, which can scan out one image for several frames, the IO has no image lag at all. This is like the CCD. Each scanned frame is crisp and unique with no history of previous information.
The effect is very pleasing to the eye. The frame rates of film and television are different. Film operates at 24 frames per second and monochrome television operates at 30 frames per second. The subject of film scanning is too complex to delve deeply into here, just understand that film seen on television has a strange motion artifact called judder.
Video camera tube
It is a sensitive tube and handling a wide range of light values and contrast. This tube makes use of the high photoemissive sensitivity obtainable from photocathodes, image multiplication at the target caused by secondary emission and an electron multiplier. It has three main sections:. A photosensitive surface, called photocathode , acting as main transducer in image orthicon camera tube. A very large negative potential i. It consists of a coating of a silver-antimony-cesium compound on the inside of the glass faceplate of the tube. When the light from an object focused on the photocathode surface by a lens system, the optical image is formed, photoelectrons, in proportion to the amount of incident light impinging, are emitted.
Video camera tubes were devices based on the cathode ray tube that were used to capture television images prior to the introduction of charge-coupled device CCD image sensors in the s. In these tubes, the cathode ray was scanned across an image of the scene to be broadcast. The resultant current was dependent on the brightness of the image on the target. The size of the striking ray was tiny compared to the size of the target, allowing horizontal scan lines per image in the NTSC format, or lines in PAL. Any vacuum tube which operates using a focused beam of electrons, originally called cathode rays , is known as a cathode ray tube CRT.