Origins of the 405 line system.

[ppppenguin]

That's a good clue. A mix would have allowed enough time for the lift to be corrected. Referring back to the M-EMI telecine, the operator would have to try to correct the lift instantly on many occasions, something that could not be done entirely successfully. Likewise tilt and bend.

Incidentally, "Birkinshaw" (not Birkenshaw) and "The Black Book" are 2 ways of referring to the same thing. The formal title is "Techincal Manual M-EMI system of Television London Station" on the cover and "Technical description of the Marconi-EMI system of television at the London television station by DC Birkinshaw MA" on the first page. My copy is 1240, issued to Cardiff.

"Birkinshaw" is not be confused with "Amos and Birkinshaw", the 4 volume set entitled "Television Engineering".

[ppppenguin]

I've just looked at this film of BBC TV from 1938, as received in New York. The pictures are very poor as you might expect but the transitions between cameras look like cuts, or if fades they are very rapid. This suggests that by 1938 they had managed to tame the lift problem sufficiently to do cuts or very fast fades.

https://archive.org/details/BbcTelevisio...wYork-1938

[Mike Watterson]

Lift was not controlled on the cameras individually in the M-EMI system.  There was a master lift control very late in the signal chain.  The racks operators (who were actually engineers, and sat at the racks i.e. bays of equipment in the Apparatus Room) controlled tilt, bend and gain. Lift was done by another engineer - and all this is in Birkenshaw.

This might be the clue as to why the vision mixer couldn't cut.  The resulting instantaneous change in lift would be impossible to correct for.

That sounds like a good explanation. Perhaps later they added it per camera, maybe on a slightly later camera tube.

[ppppenguin]

I think the first British camera tube to have decent black level performance was the post-war CPS Emitron http://www.tvcameramuseum.org/emi/3lens/p5.html

Earlier tubes were high velocity types that suffered all the usual problems.

My copy of the Black Book has handwritten notes that suggest the fade time was reduced from 2.5s to half a second, though by what date I have no evidence. This may have been some fine tuning of the mixer system plus improved operator skills. I don't have any evidence that lift controls were added on a per camera basis but that doesn't mean it didn't happen. The producers of the time must sorely have wanted to be able to do cuts, for purely artistic reasons.

[Brianc]

I missed the later parts of this thread which concerned transitions between cameras in the early days at AP. According to Norman Green, the EMI historian, the first transitions were fade-to-black, cut to next camera then fade-up. It was after further development that a cross-fade could be performed. I will speak with Norman to find out what were the technical difficulties involved in a crossfade at the time.