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Old 4th Dec 2015, 9:32 am   #1
Panrock
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Default 'Baird' 240-line aspect ratio

The Marconi-EMI 405-line standard originally used a 5:4 picture aspect ratio. I believe it was in 1949 or 1950 when it changed to 4:3. Feel free to correct me about this.

But what about the Baird 240-line standard, present only in 1936-7 ? Did this match the original 405-line picture shape at 5:4? Or was it 4:3, as is stated in the list of standards in Darryl's World Converter manual?

Not many will know the answer to this, so if you do know - please speak up. Many thanks,

Steve
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Old 4th Dec 2015, 10:38 am   #2
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Default Re: 'Baird' 240-line aspect ratio

Good question Steve.

Since I am trying to make a simple one-pattern 240-line test pattern generator, I was wondering this myself.
In "Television up-to-date" by Robert W. Hutchinson, on p.178 the following is stated:
Baird's picture-ratio follows the custom of the cinema, viz. 4:3 (after allowing for synchronizing pulses, etc),.... The E.M.I. differs slightly from this, being in fact 5:4.
The book is dated Dec.1935, but the quoted text comes from an appendix "A few points about the high definition television signals from the Alexandra Palace", so this revised issue of the book must have a later date, and represents the actual transmission standards from AP.

I have not seen a pre-war TV with an aspect ratio of 3:4, so with the Baird transmissions a few percent of the width of the picture was lost, when correctly adjusted.
Several late '40s sets seem to wander in the direction of 3:4, like the Philips 385U.

As far as I know, the change-over from 4:5 to a 3:4 aspect ratio of transmissions happened in April 1950.

Since most program material we have is in 3:4 ratio, and the old CRT-masks are 4:5, we have a dilemma on our hands.
For a standards converter a 3:4 aspect ratio would be most practical, but for a test card 4:5 could as well be chosen, is you start from scratch.
My Aurora single standard converter has a TCC with an aspect ratio of 3:4.

I couldn't yet find a picture of a decent Baird test card that would do for a test-card generator...

Hope this helps a bit.
Jac

Last edited by Jac; 4th Dec 2015 at 10:45 am.
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Old 4th Dec 2015, 10:46 am   #3
FERNSEH
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Default Re: 'Baird' 240-line aspect ratio

The aspect ratio of the Baird 240 line system was 4:3 and the Marconi-EMI system was 5:4.

DFWB.
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Old 4th Dec 2015, 11:04 am   #4
peter_scott
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Default Re: 'Baird' 240-line aspect ratio

I have an advert for a T5 and it describes the screen as 12" x 9".

Peter
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Old 4th Dec 2015, 11:21 am   #5
Jac
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Default Re: 'Baird' 240-line aspect ratio

Thanks Peter,

You're absolutely right.
The format given by EMI for the 904/706 is also strange: 4.75 x 4 ", which is even further away from the 4:3 ratio than 5:4.
Although with the visible round CRT, you could adjust to almost any aspect ratio.
Most manufacturers quote the visible size as 5:4, but certainly not all.

Jac
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Old 4th Dec 2015, 5:53 pm   #6
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Default Re: 'Baird' 240-line aspect ratio

Pretty conclusive then.

Thanks chaps!

Steve
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Old 7th Dec 2015, 3:09 am   #7
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Default Re: 'Baird' 240-line aspect ratio

Quote:
Originally Posted by Jac View Post
As far as I know, the change-over from 4:5 to a 3:4 aspect ratio of transmissions happened in April 1950.
The aspect ratio change was announced in Wireless World 1950 March (page attached) as happening shortly.

Cheers,
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