Museum of the Broadcast Television Camera

The 1948 Olympic Television Cameras

There has been some interest in the television cameras that were used for the 1948 austerity Olympics, so I have written some notes that may be of use.

Television in the Great Britain of 1948 was very different from today and the importance of televising the 1948 Olympics could be judged by the space reporting the televising of them in the BBC yearbook of 1949, less than one page!

The BBC had 3 Outside Broadcast vans, or scanners as they were known, available by the start of the Olympics on July 29, but only one of the pre war vehicles and the new EMI CPS OB vehicle were used. [Pawley 404] Six cameras were deployed, three from each of the OB vans.

The second prewar OB van, MCR2, was covering the athletics from White City on Thursday and then the test match from the Oval on the Saturday. There was some exchange of cameras between MCR1 & MCR2.


3 types of camera were used:-
One 1937 Emitron, two of the improved 1937 Super Emitron and three of the new in, 1948, CPS* Emitrons. Recent information received, leads me to think there were three Super Emitrons, two of the curved back style and at least one of the square back style as illustrated below.

1937 Emitron
The 1937 Emitron

This is the Long Necked version of the Emitron from 1937. The Emitron cameras started life with the "short neck" tubes, and later they were modified to take the improved "long necked" tubes. The cameras now had a bulge at the front to accommodate the extra tube length. It had a sensitivity of the order of 2500 Lux @ f3. The Emitron tube with its spherical glass enclosing the large target meant that the lens was a long way in front of the target and this placed constraints on the usable focal lengths and the depth of field in particular. “The older cameras were used in the stadium as they require much more light for satisfactory operation” [BBC yearbook]

Super Emitron
The Super Emitron

 


The Super Emitron had an Image Section in front of the target and this meant that the image from the lens was formed on this smaller photo target which was much nearer the lens thus removing many of the constraints suffered by the Emitron lenses. Additionally it was some 10 times more sensitive (200 Lux @ f2) enabling the use of telephoto lenses in poor light conditions. The Super Emitron tubes were retro fitted into 2 of the cameras and these had modified housings to accommodate the different shape tube. The bulge on the camera front now became a bulge on the side. It was necessary to rotate the whole tube to correct for the image rotation between the photo cathode and the target. It is not clear how many Super Emitron cameras there were, I have been able to identify 2 case styles, curved and square backed. (illustrated)


Post War 3 lens Emitron
The CPS* Emitron

 

 

 

 

The CPS Emitron tube was of the orthicon class and the target was at the front of the tube, optically good for the lenses. It was scanned orthogonally from the rear so no keystone distortion and it was also said that the CPS Emitron tube was free of the shading problems of the Emitron tubes. The tube was even more sensitive about 100 Lux @ f2 was required.
The instability known as "peeling" was a problem for the early tubes. It was caused by a bright object in the field of view, a lamp, or bright specula reflection overloads the tube. Photographers flash bulbs were known to be a serious problem. Once a tube started to peel little could be done until normal operation could be recovered. Later cameras (1950+) had a compensation circuit to automatically reset the tube and later CPS Emitron tubes were free of the defect.

*CPS = Cathode Potential Stabilised

Link to EMI CPS Emitron cameras in action on BBC site. (external)

Both the Emitron and the Super Emitron tubes suffered from shading (an effect similar to lens vignette or portholing, but much more pronounced and unpredictable) and other spurious signals. Correction waveforms had to be added to the picture signal to attempt to alleviate the shading. These waveforms were called "Tilt and Bend" and required frequent adjustment. Additionally because the target was scanned from the side the beam that scanning the target had to have corrections added to it to correct the distortion known as keystone distortion.

This 405 line image is before correction.

Notes:- BBC OB vehicles had a designation number starting with MCR1. MCR = Mobile Control Room. They were known informally as scanners. The American term is "Remote Unit".