Talk:Video camera tube

Orthicon & tube sizes

One item that has not been discussed is the relative size of the various camera tubes. This is not much of an issue for studio cameras, but can be of considerable concern for portable cameras.

Typical Image Orthicons are rather long (approximately 18 inches), while Vidicons are typically only a few inches long. Additionally, Image Orthicons are typically many inches in diameter (3-4.5 inches), while Vidicons may be less than an inch in diameter. The result is that cameras using Image Orthicons are typically rather huge boxes, while cameras using Vidicons may be held in the palm of a hand.

Another issue that has not been addressed is the ruggedness of the various tubes. Image Orthicons can be quite fragile. The target plate in an Image Orthicon is made from glass and is quite thin, which results in it being rather fragile. The target must be of an insulating material, and thin enough that electric charges deposited on the front of the tube by the photoemitted electrons can migrate through the thin layer to the back of the target, where they will be scanned by the electron beam. One of the cautionary notes about the operation of Image Orthicon tubes states that they should never be pointed with the face below about a 30 degree angle. This is to prevent any debris, which may be present at the back of the tube as a result of the manufacturing process, from sliding forward along the neck of the tube and impacting the target, since such an impact, even by a tiny bit of debris, is likely to shatter the target.

Another cautionary note involves the operating temperature of Image Orthicons. The photoemissive layer at the front of the tube is somewhat volatile. Thus, the tube should never be subjected to operation in temperatures at which the photoemissive material could evaporate, since it would likely be deposited on the target, which would ruin the charge storage mechanism that the target operates on. A similar effect can be produced by excessive illumination. Thus, an Image Orthicon should never be aimed, even momentarily, such that its view images the sun or a bright light, since the energy focused on the photoemissive surface may be intense enough to cause evaporation of the photoemissive material.

A counter-effect is that the characteristics of the photoemissive material are somewhat temperature sensitive, which means that Image Orthicons may lose some sensitivity in cold temperatures. Thus, some camera equipment which used Image Orthicons would provide a heater to warm the front of the tube in cold weather.

Dave

Iconoscope's sensitivity

The iconoscope section needs some work. Larger "lux" values indicate less sensitivity. "75,000 lux" is a terrible sensitivity. Tropical noon sunlight is around 100,000 lux.

That number can't be right. It's all over the web, but it has to be wrong. The source of this misinformation seems to be http://www.akh.se/tubes/camera.htm . Iconoscopes were insensitive, but not that insensitive, at least in their later forms.

It should be mentioned that the image orthicon combines the advantages of the image dissector and the iconoscope. The orthicon was the first tube that had decent sensitivity.

--Nagle 18:50, 11 March 2006 (UTC)[reply]

In re this question, it seems possible that what is meant is that a light source of about 75klx intensity is required for a decent image. Having taken photographs of stage-lit events I can confirm that the light intensity is usually comparable with cloudy daylight, and stronger lighting is certainly possible. It does seem unlikely that what is meant is that the tube could only register--as a minimum--signals of 75klx.

It is also possible that the article refers to the first tubes only.

The datasheet for the RCA 5820 Image Orthicon, states "Commercially acceptable pictures can be obtained at incident light levels greater than about 10 foot-candles". So unless I am wrong, that means: 10fc = 107.64 lux I couldn't find the sensitivity of the RCA iconoscopes, however while 75klx is simply ridiculous, anyway in Radio Engineering by Terman (1947) it states that the IO's sensitivity is between 100 and 1000 times more sensitive than the iconoscope. So the current value of 75lx is even better than the IO :) Something is plainly wrong. Alchaemist (talk) 04:34, 13 March 2009 (UTC)[reply]

The datasheet for the RCA 5820 Image Orthicon, states "Commercially acceptable pictures can be obtained at incident light levels greater than about 10 foot-candles". So unless I am wrong, that means: 10fc = 107.64 lux is pretty near the 200lx as described generally in [1]. While the RCA 1848 iconoscope says "Good operation can be obtained with a highlight illumination level on the mosaic in the order of 7 foot-candles", so roughly 75lx, NOT 75Klx (perhaps there was a typo or a conversion error). However, this appreciations are subjective, because that would mean that the iconoscope was more sensitive than the IO, which is completely impossible. My best guess is that simply what was considered good in 1940 was not in 1950s. According to Terman in Radio Engineering, IO should be between 100 and 1000 times more sensitive than the iconoscope. Alchaemist (talk) 04:34, 13 March 2009 (UTC)[reply]

Alchaemist -- do not confuse SCENE illumination, the light falling on the subject and TARGET illumination, the light collected by the lenses and delivered to the tube's target.

I am looking at the original paper data sheet from the published and readily available RCA HB-3 Handbook, for the 5820 Image Orthicon dated Sept 15 1949, Its states "...illumination on photocathode for maximum signal Output: 0.01 ft-c" You can find a sheet from Philips for their 5820 at http://tubedata.milbert.com/sheets/030/5/5820.pdf stating similar values.

The data sheet, same source, for the RCA 1850-A Iconoscope states that the required illumination on the target should be between 4 and 20 ft-c.

The Iconoscope is about a thousand times less sensitive than an Image Orthicon. To convert foot-candle to lux multiply by 10.8 OldZeb (talk) 05:39, 15 March 2009 (UTC)[reply]

Orthicon or Image Orthicon

My recollections of camera tube types are that there is a difference between the "Orthicon" and the "Image Orthicon" tubes. The Image Orthicon was developed out of the Orthicon tube which was invented by Arthur Rose in 1937/38. The Orthicon had no what we used to call "Image Amplifier" located in the larger section at the front of the Image Orthicon tube. So, for the article to be correct, the heading “Orthicon” should really be changed to “Image Orthicon”, the words "or simply orthicon tube" removed and another heading and description for its ancestor the “Orthicon”. I’m having a problem locating technical information about the Orthicon (sans Image) tube but I found a diagram and a bit more information at: http://members.chello.nl/~h.dijkstra19/page4.html and an IEEE reference at: http://www.ieee.org/organizations/history_center/legacies/rose.html. In Australia we were using Image Orthicon cameras at least into the 1970's. Fernseh brought out the only solid state Image orthicon camera I know of in about 1968. We referred to the tubes as "IO's". Peter Resch 06:39, 28 April 2006 (UTC)[reply]

Elaboration on above comment and 'emmy' correction

The nickname 'emmy' came from another tube from the same family, the Emitron (or CPS Emitron). (for more, see http://www.burle.com/cgi-bin/byteserver.pl/pdf/pctdhbook.pdf which is based from original source material, see its footnotes) The Image Orthicon, or IO, and the emitron, or CPS Emitron, both used a mosaic type photoemitter.

Regarding the comment above, I believe he's talking about the earlier Multiplier Orthicon. The MO tube had an electron multiplier in it that amplified the signal prior to sending it to the video amp so as to produce a stronger but still relatively clean input signal. But the IO tube also had a multiplier built in for the same purpose, but also had a two-sided target. And both were sent to a video amplifier. The multipliers were to boost the weak source signal. On principle I agree with the notion of making the heading just 'Orthicon', but generally when people talk about orthicon tubes, they're talking about IO tubes as they were the more advanced and in more widespread use.

140.247.121.204 (talk) 15:18, 20 March 2008 (UTC)[reply]

A not so tiny detail

I'd like to see this article explain how it's possible to have a beam going from electron gun to target and then have a return beam. If high voltage is what accelerates the beam one way then I'm confused how a beam can then go the other way. That's the sort of thing that's glossed over and I'd be very curious about. Steve / filmteknik

Steve,

The electrons will land on the target only as long as the target potential is higher than the cathode potential. All remaining electrons are either reflected or scattered depending on their arrival energy and return towards the cathode. Most will be captured, however, by the aperture electrode, which is beloe cathode potential. It is at this point that electron multiplier structures can be inserted to read out the return beam as is done in image orthicons (read the reflected beam) and isocons (read the scattered beam.

Dave Gilblom

Vladimir Zworykin vs Philo Farnsworth

This article gives primary credit to Vladimir Zworykin and minimizes the contribution of Philo Farnsworth in the invention of the television camera. Farnsworth is responsible for the key idea of using a 2 dimensional matrix of photosensitive material to create the electronic signal. Zworykin, backed with the resources of RCA, improved on Farnsworth's ideas and created the iconoscope. Although Zworykin/RCA attempted to claim the entire invention, the US patent office found in favor of Farnsworth and RCA was required to pay royalties to Farnsworth for his patents. Farnsworth version of the story can be found here http://www.farnovision.com/chronicles/tfc-who_invented_what.html http://www.farnovision.com/chronicles/tfc-intro.html Zworykin/RCA version of the story can be found here http://www.acmi.net.au/AIC/ZWORYKIN_BIO.html

Kharkless

I am sorry to say this but the idea of using a 2 dimensional matrix of photosensitive material goes back to Alan Archibald Campbell Swinton who presented this idea in the paper Distant Electric Vision printed in the journal Nature 78, 151 (18 June 1908), several years before Farnsworth. You can find a copy of this paper in the web page:

http://www.nature.com/nature/journal/v78/n2016/pdf/078151a0.pdf.

Even in Farnsworth's wikipedia file it is textually said: [In 1930, after a visit to Farnsworth's laboratory, Vladimir Zworykin copied this apparatus for RCA, though he found it impractical and returned to his work on the iconoscope. The U.S. Patent Office rendered a decision in 1935 that the "electrical image" of Farnsworth's image dissector was not in Zworykin's inventions, and priority of that invention was awarded to Farnsworth].

RCA indeed paid in 1939 one million dollars for Farnsworth's patent on the "Electrical Image" concept because they needed the patent rights to produce their Image Orthicons (built by Rose, Law, and Weimer in 1944-1945). The image part (photocatode and target) in the Image-Orthicon is indeed a Farnsworth's Image-Dissector, but Zworykin's Iconoscope does not use any "Electric Image" as the U.S. Patent Office dictaminated. Zworykin used Tihanyi's ideas, but not Farnsworth's ones. —Preceding unsigned comment added by 189.216.171.103 (talk) 05:08, 10 March 2009 (UTC)[reply]

Plumbicon Tubes

In the TV series Monty Python's Flying Circus, they used EMI 2001's with Plumbicons. In one episode, Episode 17, a model of a building exploded and caused the camera to show a glowing red and green halo and then it faded away. Was this a malfunction? Curvebill 18:48, 9 September 2007 (UTC) by abhinav —Preceding unsigned comment added by 59.93.70.119 (talk) 16:51, 19 October 2008 (UTC)[reply]

Image Orthicon copy-edit

I rewrote the subsection Operation of the Image Orthicon to be more precise and accurate. I based myself in Radio Engineering by Frederick Terman from 1947. I would like to cite it as a source, however it applies to the whole subsection, rather than a part of it, so I don't know where to put it. Finally, I don't think the copy-edit note should stay for the Image Orthicon section, what do you think? Should we remove it? Regards! Alchaemist (talk) 03:57, 13 March 2009 (UTC)[reply]