EMI 2001
The EMI 2001 Broadcast Video Camera was an early, very successful British made Plumbicon video camera that included the lens within the body of the camera. Four 30mm inch tubes allowed one tube to be dedicated solely to producing a relatively high resolution monochrome signal, with the other three tubes providing red, green and blue signals. Even though semiconductors were used in most of the camera, the highly sensitive head amplifiers still used thermionic valves in the first generation of the design.
Integrating the lens within the body of the camera had both positive and negative effects. On the positive side, it meant the optical nodal point of the camera was close to the centre of gravity, which could make operation easier and more instinctive when used on movable camera mounts such as pedestals. The downside was that lens manufacturers were limited to which lenses they could adapt to fit to the camera. This made the 2001 less attractive for outside broadcasts.
The 2001 was both heavy and large. The pull-out handles at each corner needed four people to safely move the camera with the lens in place. It also required a separate remote camera control unit and the cable connecting the two was over 2" thick. The standard servo controlled studio zoom lens had a 5 to 50 degree horizontal angle of view, with a minimum focus distance of either 36" (J type) or 18" (K type)
First produced in 1966, by the early 70's almost all of BBC TV's studios and many OB units were equipped with the 2001, along with many ITV studios. It was still in use until July 1991 producing "Eastenders" at the BBC Elstree Studios. You can see the camera in vision on many of the posted pop music clips from the late 60's to the mid 80's.
The EMI 2000 (as it was originaally called) that was originally tried and tested by the BBC in 1967 used 30mm. integral mesh lead-oxide vidicons (Ledicons from EEV)(Plumbicon is the trade mark for Philips lead-oxide tubes) It also used a themionic valve for the first stage of the video head amplifier. Unfortunately, the BBC technicianss were disappointed by the picture results. So disappointed in fact that they hesitantly bought 17 Marconi Mk VIIs in order to commence colour broadcasting on BBC2 on July 1st 1967 as the redesigned and re-named EMI 2001 would not be ready for the colour launch date on BBC2. EMI re-released the re-named 2001/1 (now with the option of separate mesh tubes, either Plumbicon or Leddicon, and solid state (FET) head amplifiers) in early 1968 and the BBC moved their Marconi Mk VIIs to the weather, news and presentation studios from TC7 and TC8 in Television Centre.
Generating the Image
Unlike most colour tube cameras of the period, which combined the output from three colour tubes at the same stage before the signals left the camera and made white light by combining the output from all three colour tubes, and the Marconi MkVII, which added the output of the three colour tubes to the output from the luminance (black and white) tube, the EMI 2001 took the ouput of the green tube as a starting point for the picture, added the colour from the red and blue tubes and then added the output from the luminance tube. Unlike the others, the luminance tube in an EMI 2001 wasn't used for taking white light, but it was used for the sharpness and fine picture detail of whatever object was the subject to be taken.[1] This image was electronically added on top after the the output from the red and blue tubes was electronically added to the green one.
This was the part of the camera's design that was designed by BBC engineers, as they realised that he most natural colour could be achieved by the method that was used by the EMI 2001.
Comet Tails
A very common artifact of early vacuum-tube cameras was a "comet tail". This is where a bright light or anything white builds up so much charge on the imaging surface of the camera tube that the charge cannot be removed in one "field" (1/25 of a second, the rate at which television pictures are made). So when the camera is moved, the object causing the bright light is moved, or something moves between the camera and the bright light source it causes a bright streak of where that light was. This is because that particular picture element on the camera tube's imaging surface is supposed to be imaging a dark surface, but it still has electric charge on that picture element and is read out by the camera as light instead.
Most models of colour television camera had ACT (Anti-Comet tail) circuits for each individual camera tube and if they are not matched precisely, the comet tails appear to be coloured rather than white. The EMI 2001s didn't have ACT circuits. This means it is often very easy to tell if a programme used EMI 2001s to capture the pictures as the comet tails would often be coloured "blobs" or "splodges" simply because they didn't have ACT circuits, but some were modified to include ACT circuits. The ACT circuits were adjusted so that the Comet Tail doesn't appear to be a "blob".
Another artifact about the comet tails produced by the 2001s was that sometimes the comet tails would either be a mix of two separate colours, one colour inside the other (e.g. a comet tail that is red with a smaller comet tail inside that one that may be green). This is where both of the (in this example) red and green ACT circuits are not to the same adjustment of the other two tubes, but are adjusted at different levels themselves. In other cases, comet tails have been produced by 2001s that are not primary colours of light, e.g. pink. This is where the adjustments of both of the (in this example) red and white tubes are not adjusted to the same adjustment of the blue and green tubes, but are both themselves placed at the same adjustment.
ACT and the EMI 2001/1. As supplied by EMI the 2001 and the later 2001/1 did not have any form of ACT (anti comet tail) or HOP (highlight overload protection). This is why it's performance was poor, in this respect, when compared with the next generation of cameras supplied in the 1970s. None of the first generation of true broadcast cameras in the middle to late 1960’s had ACT, so the EMI 2001 was not unusual.
It may be that some studios later modified their cameras to have ACT. So I have not changed the above descriptions. Retro fitting ACT/HOP is not an easy modification as 4 new HOP camera tubes would be needed, the tube bases, wiring harness, 4 head amplifiers and 4 video amplifiers and the tube beam current boards would all have needed work done. ACT and HOP works by using an extra electrode in the tube to “flood discharge” the target during the flyback period. Great care was needed in setting up the HOP voltages as damage to the tube’s emission could occur.
There was another method, ABO or DBO (Dynamic Beam Optimisation) that worked by measuring the tubes output and if it is more than a pre-set level above peak white, increasing the beam current in proportion. This DBO method could be used with standard tubes. If this is not implemented well it can lead to positive feedback, with loss of picture and damage to the tubes.
References
- ^ This led to the configuration of tubes being referred to, humorously, as "red, green, blue and viewfinder" by some within the BBC.
"The EMI Four-Tube Colour Camera" published in the Radio and Electronic Engineer, Vol.39 No.5 May 1970. Pages 249 to 270.