Found this website which describes the origins of the 625 line system. My apologies if it has been posted up before.
We are told how in 1944 the Russians explored various proposals for a television system which could match the quality of 16mm film.
The website:
https://medium.com/@ReflectiveObserver/f...d02007e22a
Geordie McBoyne.
I think our antipodean friend, Synchrodyne, explored this in some detail a while ago.
There was an obvious need for an odd number of lines (for interlace) in the range 500-700 that is a product of small integers. This last criterion was for ease of sync pulse generation before modern logic. 625 meets this nicely with 5x5x5x5. 525 and 567 are OK too but were rather low points to aim at in the 50Hz world. 729 and 735 were aiming a bit high. I don't think there are any other obvious candidates apart from 675. You can arrive at 625 simply by aiming for the middle of the possible numbers.
As others have said, it roughly matches 16mm film capability, though under optimal conditions and modern emulsions 16mm can do better than 625 TV.
I know hindsight is a wonderful thing and in retrospect it's obvious but was it obvious at the time?
I think the argument about almost common line scan rates for 525 and 625 is spurious. It didn't matter at the sending end. Only place it matters is the receiver line scan. By then it was perfectly easy to design for any required rate up to at least 20kHz. The time it mattered was much later in standards conversion and setting the first "601" digital standard. For both of those the close line rate turned out to be a simplification.
Not forgetting the 605 line system suggested by EMI. Can't find any published specifications anywhere for this TV system.
Also Cossor with their 525 line system which could be squeezed into a system A channel bandwidth.
Geordie McBoyne.
605 = 5 * 11 * 11 Not such a good idea with early dividers.
Should have said a bit more in previous post. 605 and 625 are so close that there's no real difference between them. 625 causes less trouble with early dividers. So why even bother with 605.
819 = 3 * 3 * 7 *13 but by then dividers were a bit easier. Doing divide by 13 the old fashioned way with locked blocking oscillators would have been very hairy.
(05-11-2020, 01:20 PM)ppppenguin Wrote: [ -> ]Should have said a bit more in previous post. 605 and 625 are so close that there's no real difference between them. 625 causes less trouble with early dividers. So why even bother with 605.
819 = 3 * 3 * 7 *13 but by then dividers were a bit easier. Doing divide by 13 the old fashioned way with locked blocking oscillators would have been very hairy.
I did wonder how the French ended up with such an odd amount of lines. Some early experiments were for over 1000 lines.
819 was definitely pushing the technology of the time. But it was a plasusible attempt, since the standard allowed headroom for the technology to improve and fully exploit the lines and bandwidth. But it didn't work out in the end. France was left stranded with 819 just as the UK was with 405.
It needed digital transmission, with powerful data compression, to move beyond 625 for everyday use. Yes, there were attempts at 1125 analogue, notably in Japan, but they never gained a critical mass.
At the studio end, I look back on the work I did designing analogue vision mixers and how hard it was to get really good results. I did just one rather simple digital vision mixer and the problems just melted away.
No doubt the Russians used modified RCA 525 line equipment for the development of the new TV system. 525 line dividers 3 X 7 X 5 X 5. Easy to adjust the counters for 625.
The modified M-EMI sync dividers used 9 X 9 X 5.
Geordie McBoyne.
(06-11-2020, 08:21 PM)Geordie McBoyne Wrote: [ -> ]The modified M-EMI sync dividers used 9 X 9 X 5.
More likely 3 x 3 x 3 x 3 x 5. EMI had been working with 343 lines which is 3^5. The story, possibly urban myth, is that that one weekend at Blumlein's house they thought it would be a good idea to change one of the 3 dividers to a 5 and this would represent a great leap forwards. The other view is that based on work RCA was doing at the time it was obviously a sensible thing to do.