EMI 2001

The EMI 2001 broadcast studio camera was an early, very successful British made Plumbicon studio camera that included the lens within the body of the camera. Four 30 mm tubes allowed one tube to be dedicated solely to producing a relatively high resolution monochrome signal, with the other three tubes each 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.

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 inches thick. The standard servo-controlled studio zoom lens had a 5 to 50° horizontal angle of view, with a minimum focus distance of either 36 inches (J type) or 18 inches (K type).

Four-tube prism optics

The EMI 2001 used a four-way prism assembly to split the light into its components, using the same novel principles that had been developed by Philips for its three-way splitter. These new assemblies used the property of total internal reflection, within the prisms, to direct the light to the pick-up tubes. The techniques were described in a patent first filed in 1961. The three-way prism was also described in a description of the LDK3 camera.

The technique of using a prism assembly in this way was far superior to the earlier light-splitting arrangements, since the prism assembly was neat and compact and reproducibility in manufacture was much improved. The problems previously experienced with double imaging (common with plate glass dichroic mirrors) were also eliminated.

Development

In 1963, prior to the development of the 2001, an experimental four tube camera[20] was constructed by EMI engineers. This experimental camera had been inspired by RCA's new four tube camera, the TK-42,[21] and used the same tube arrangement, i.e. a 4+1/2 in image Orthicon tube in the luminance channel and three 1 in Vidicon tubes in the colour channels. In addition, the experimental camera had an integrally mounted Varotal III zoom lens. It was demonstrated to the BBC in 1964[22] where it received a mixed reception. Pictures from the camera had disappointing colorimetry, but sharp luminance detail.

A production version of this camera was planned, the EMI 2000, but this camera was never built after the BBC had initially specified Vidicon tubes. Before production, the BBC changed policy to adopt the newly available Plumbicon tubes[23] supplied by Philips, in the new camera, the EMI 2001, which delayed production as design revisions were necessary to accommodate the performance parameters of the new tubes in the circuits that they would be integrated with.

Operational history

First produced in 1966, by the early 1970s almost all of BBC Television's studios and many outside broadcast (OB) units were equipped with the 2001.[37] Several ITV companies purchased or leased the camera including Thames Television, Yorkshire Television, Associated Television/Central Independent Television, Granada, HTV, Anglia, London Weekend Television and Independent Television News. Independent outfits such as the early cable television stations Rediffusion Cablevision, Sheffield Cablevision and the educational television arm of the Inner London Education Authority also purchased the camera.

When sold abroad, the EMI 2001 was carried under the Thomson SA brand – hence "Thomson TH.T 2001". How this came about is unknown as EMI and Thomson SA did not have business links.

The Thomson 2001s, like the EMIs, also used Plumbicons; however, due to a brochure which was printed in French, it was presumed that they used Vidicon tubes.

Zoom lenses for the 2001

Rank Taylor Hobson declined to offer a zoom lens for EMI's new camera, claiming it was fully committed elsewhere, but Angenieux (see Pierre Angenieux) expressed its interest in supplying zoom lenses for the project. The French company offered two zoom lenses for the camera; the first was a 10:1 zoom for studio use and the second a larger unit for outside broadcasts. Both could be accommodated within the body of the camera, although the O.B. lens did protrude a little. To accommodate a four-way prism splitter, extra distance was needed from the back of the lens to the image focal plane, when compared with a three-tube splitter. This set severe demands for the lens designer, but Angenieux was able to achieve EMI's requirements, provided that field flattening lenses were fitted in front of each pick-up tube. Early cameras used this arrangement, but with later zoom designs these lenses became unnecessary.

The servo motors and the servo amplifiers were supplied by Evershed Power Optics.[43] The driver amplifiers for the servo motors were mounted in the camera body alongside the lens. The servo-driven zoom lens and the associated amplifier circuitry added considerably to the weight of the camera. In addition, incorporating the servo drivers within the camera body precluded the use of other makes of zoom lens.

Benefits of an integral zoom lens

The integral zoom lens was a popular feature of the EMI 2001, which was liked by camera operators, and it was sometimes referred to within the television industry as "the cameraman's camera".

External links

Demonstration of EMI 2001 'lining up process by ex BBC OB operators
Ex BBC OB camera operators discuss their experience working with the EMI 2001
BBC Tech Ops History Site
Museum of the Broadcast Television Camera
The website of Martin Kempton on London television studios contains much on the industries use of various cameras over the decades, including the EMI 2001.

References

{{US patent reference | number = 3202039 | issue-date = August 24, 1965 | inventor = de Lang H. & Bouwhuis G. | title = Optical System for a Colour Television Camera }}^
Summers B. "Museum of the Broadcast Television Camera", Soviet Television Cameras^
Fink D.G., "Television Standards", Television Engineering Handbook, (Ed. Fink D.J.), Chapter 2, McGraw Hill 1957, pp. 2-1 to 2-54^
Mazda F.F.(ed.) "Colour Television Principles", Butterworths, 1989, Section 53.9.2, pp.53/10 to 53/12^

Generating the image

The composite signals of the NTSC, PAL and SECAM systems are made up of a wideband luminance signal and two narrow-band colour difference signals containing B-Y and R-Y. If a band-limited version of the signal from the luminance tube is used to derive the colour difference signals, without modification, then colour errors would occur. This is because the luminance characteristic expected by the colour processing must be made up in a particular way, using specific proportions of red, green and blue, whereas the signal from the luminance tube has a more general monochromatic characteristic akin to that from a conventional black and white camera. In addition, the application of gamma correction to the signals further complicates the situation (display tubes have, approximately, a square law characteristic with γ ≈ 2.2).

As shown below, it is beneficial, but not sufficient, to shape the luminance response to simulate that of the NTSC (PAL or SECAM) luminance characteristic (by, for example, placing an optical filter in front of the luminance tube to pass light with the required luminosity function, or by a special dichroic surface which reflects light to the luminance tube with the required luminosity function).

For a basic 3-colour system the wideband luminance signal (Y'), for NTSC, PAL and SECAM, is given by:[3][4]

In the case of a separate luminance tube, with appropriate spectral shaping, the output signal (Y) is given by:

which when gamma-corrected gives:

When deriving the two narrowband colour difference signals containing RN and BN, a bandlimited version of the luminance signal (y') is required, namely:

but the band limited signal from the luminance tube is:

As before, does not equal y'. If the gamma corrected luminance signal is simply used instead of y' then colour errors result which can be appreciable for saturated colours.

In the EMI 2001 a process known as Delta-L Correction[5] is used to overcome this problem.

A band-limited luminance difference correction signal, ΔL is formed, where: This narrowband signal is used to correct the wideband luminance channel at low frequencies, so the monochrome signal transmitted becomes:

With this corrected luminance signal, the correct colour rendition is obtained, whilst still retaining the sharp luminance detail of a 4-tube camera. The narrowband R, G and B signals are gamma corrected and applied to a suitable matrixing circuit, to derive the correction. With grey scale scenes = y' and the signal reverts to that of the luminance tube only.

does not equal Y' except when R = G = B, which corresponds to neutral (grey) tones.

EMI's experimental 4-tube camera

EMI engineers visited the United States in 1963, in order to view RCA's new four-tube colour camera, the TK42.[28] Immediately following this visit, EMI Research Labs. embarked on a program to build an experimental camera using the same format. The construction took only six weeks of intensive effort, aided by the cannibalization of parts from existing EMI cameras. Items were taken from an EMI Type 203 image Orthicon monochrome studio camera,[29] for the luminance channel, and a Type 204 industrial colour camera,[30][31] for the colour channels. This camera contained three Vidicon tubes and a colour-splitting system using plate glass dichroic mirrors. In addition, a Varotal III zoom lens was integrated into the body of the experimental camera. The camera was housed in a simple box-shaped structure with ribs of extruded aluminium and plain side panels.[32] The experimental camera was demonstrated to the BBC in 1963 where it received a mixed reception. At that time, the BBC was evaluating an early Philips three-tube camera which used some newly available Plumbicon pick-up tubes.[33][34] It had been set up by BBC engineers to give highly saturated colour pictures and they were unimpressed by the 'tinted' pictures of the EMI camera. In order to better judge the performance of the then existing cameras, the BBC organised comparison tests between the experimental EMI camera, a Philips camera and a Marconi three I.O. camera.[22] In these tests, the colorimetry of the pictures from the EMI camera compared unfavourably with the other two, but it did give the sharpest pictures.

The development of the EMI 2001

In spite of the BBC's lukewarm reception of the experimental camera EMI persisted with the four-tube concept, but now using Plumbicon tubes, as suggested by Wood[22] although there was some delay before the work started. There were several reasons for the delay. Firstly, EMI's board hesitated to provide the financial investment needed for the project. Secondly, there was indecision regarding where to place the work but, eventually, the Colour TV Department of the Research Labs. was chosen in preference to the Broadcast Equipment Division (the existing supplier of EMI's monochrome cameras and studio equipment). Thirdly, there was concern regarding the reliability of supply of Plumbicon tubes, as Philips was the only supplier. Fourthly, there were concerns regarding the variable quality standards of the early Plumbicon pick-up tubes, as some tubes were found to produce unstable pictures.[22] Although most issues with tube quality were quickly resolved by Philips, there remained concerns regarding 'comet tails' and 'blooming'.

After the EMI board granted approval for the new camera, in late 1964, work on it progressed rapidly. The camera was to use four Plumbicon pick-up tubes and solid state circuitry, include a zoom lens as standard and to use prism optics. After the late start, the first fully operational prototype was shown to the BBC and others in 1966, only just in time to meet BBC time-scales for the introduction of its new colour service.

Early cameras used thermionic valves (vacuum tubes) in the first stages of the head amplifiers but later FET amplifiers were introduced, such cameras being designated type 2001/1.

Design

Four-tube prism optics

Development

Operational history

Zoom lenses for the 2001

Benefits of an integral zoom lens

See also

External links

References

Generating the image

Transistor circuits – the ring-of-three

Band defining linear phase filters

Comet tails and blooming

ACT and the EMI 2001/1

EMI's experimental 4-tube camera

The development of the EMI 2001