30 or 32 ?

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30 or 32 ?

Postby Viewmaster » Tue Apr 17, 2007 2:55 am

I am a little confused.....
The Baird standard was 30 holes. The NBTVA club standard is 32 holes.
Yet this shot recently shown on this forum by Klaas......
http://www.taswegian.com/NBTV/forum/viewtopic.php?t=135
shows a 30 hole disc.

I wonder whether many are making non club standard discs of 32 holes?
You see, my drill is itching to start drilling but it doesn't know whether to go for 30 or 32 ?
Albert.
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Postby DrZarkov » Tue Apr 17, 2007 7:02 am

I prefer the club standard for two reasons: 1. The format 3:2 instead of 7:3 seems to me much more "normal".
2. It is easy to make a monitor for horizontal scanning and vertical scanning. Even if it is not the "real" german standard (it doesn't matter, there aren't any old videos left...), it is still interesting to do experiments with advantages or disadvantages of horizontal or vertical scanning. So my "luxury TV" will be like the Telehor, to enjoy both systems.
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Scanning lines.

Postby Stephen » Tue Apr 17, 2007 7:52 am

If I were building from scratch my preference would be the Baird 30 line standard. Not only is it historical, it offers better resolution with 30 by 70 pixels instead of 32 by 48 pixels. By simply panning the camera or having subjects move back and forth in front of the camera one can overcome any limitations of the narrow aspect ratio. Furthermore two of the three club CDs include material in both formats.
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Re: Scanning lines.

Postby Viewmaster » Wed Apr 18, 2007 12:41 am

Stephen wrote:If I were building from scratch my preference would be the Baird 30 line standard. Not only is it historical, it offers better resolution with 30 by 70 pixels instead of 32 by 48 pixels.


Yes, I favour history too. That's why I voted for all mechanical with just a little electronics.
But I believe that in the Baird standard, to be historically correct, the first and last 3 lines have a wider spacing and so for a beginner like me, that may be a line too far. :)
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30 or 32

Postby Stephen » Wed Apr 18, 2007 1:59 am

I wonder if anyone really builds scanning elements that really have the first and last three lines so spaced. Also, the aperture size would have to be correspondingly larger for these lines. I also wonder if the source material on the club CDs really follow this standard precisely. I am not even clear if the Baird cameras themselves had this sort of spacing or if it was just in the televisors to give the appearance of a wider display.

In any case, you could fabricate a scanning disc with evenly spaced and sized apertures and then use optics to provide such an effect. For instance, many rectangular reading glasses tend to magnify slightly more along their sides due to lens design and this you could use to enlargen the side lines with proper placement. You would have to find an appropriately sized rectangular reading glass to do so.
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30 and 32

Postby Stephen » Wed Apr 18, 2007 2:06 am

For your further drilling enjoyment you could have a disc with inner and outer spirals, one for the 30 line standard and the other for the 32 line standard. Then you could either shift the disc motor platform or the optics platform for viewing either system. You could likewise have another spiral for the 30 line German standard and have additional optics along the top of the disc for lateral scanning.
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Postby Klaas Robers » Wed Apr 18, 2007 6:54 am

The 30 line discs that Denis made are intended for his replicae of Baird Televisors and Daily Express monitors. I think that only if you want to make a "perfect" replica of some vintage equipment, that 30 lines is a reasonable choise.

The disc Denis was punching have indeed the wider rectangular holes and a wider spacing for the first and last 3 lines. When you are doing things perfect, then they should be perfect. The 3:7 aspect ratio implies a more narrow spacing and smaller holes than the 32 line "Club standard".

The 30 line video phragments of the club-CDs have still a 2:3 aspect ratio, there is a much longer black period around the sync pulse. The extra wide lines are indeed anticipated, at least at CD 3. This gives almost the same width as 32 lines, although the borders have less definition. The special 3:7 aspectratio (in practice because of the wider lines and the sync pulse almost 2:1) cannot be experienced.

Another difference is that the 30 line video has no frame identification, while the 32 line video has the missing line pulse. If you want to experiment with automatic frame synchronisation then this cannot be done with the 30 line video.
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Re: 30 or 32

Postby Dave Moll » Wed Apr 18, 2007 8:52 pm

Stephen wrote:I am not even clear if the Baird cameras themselves had this sort of spacing or if it was just in the televisors to give the appearance of a wider display.

A precursor of the "stretchyvision" often used these days to force a 4:3 picture into a 16:9 screen :D
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30 or 32

Postby Stephen » Tue Apr 24, 2007 10:04 am

I suspect that "stretchyvision" was indeed involved here. My reason for saying so is the technology used for the live telecast of the Epsom Derby in 1931, wherein the camera scanned a 90 by 70 pixel image in three segments. The middle 30 by 70 pixel segment was broadcast whilst all three segments were sent by wire for 90 by 70 pixel "wide screen" theatre viewing. If the sides of the middle segment had wider spacing and therefore less resolution that would have adversely affected the three segment theatre presentation.
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Stretchyvision.

Postby Stephen » Wed May 09, 2007 8:08 am

The later Baird televisors had mirror drum scanners for which there would have been no convenient way to change the size of the scanning lines for the first and last three lines with them. I have attached a picture of such a Baird televisor with a projected display that appears to have the long 3:7 aspect ratio. The studio cameras had mirror drum scanners as well. I suspect then that only the disc scanning televisors may have had the wider apertures for the first and last three lines as a means of conveying a slightly wider display image, even though somewhat distorted.
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