09-05-2020, 05:06 PM
I would have expected 8 lines of distortion to be visible on a test pattern. Especially the way Peter has shown it.
I've seen 240/25 on a pre-war TV and also on a modern-ish monitor. The picture looks fine but the flicker is horrible. The video BW of a 240/25 signal is about half that of a 405/50i signal. This gave the entire video chain from camera to CRT a much easier job. Pictures tend to look sharp. 3MHz or so BW was possible then but not easy. Also 405/50i gave 405 lines only on still pictures. As soon as anything moves the effective vertical resolution drops to 202 lines. This is ignoring aperture effects and Kell factor.
The problem was that 240/25 was really pushing things with mechanical scanning, apart possibly from the telecine. I'm sure Baird himself and BTL (JLB was no longer directly involved by then) that mechanical scanning had run out of steam, hence their work with the Farnsworth "electron camera". Also all receivers except Scophony were fully electronic, again bowing to the inevitable. 240/25 as a standard gave no headroom for improved kit to give better pictures. 405 amply demonstrated that it could benefit from newer technology.
I've seen 240/25 on a pre-war TV and also on a modern-ish monitor. The picture looks fine but the flicker is horrible. The video BW of a 240/25 signal is about half that of a 405/50i signal. This gave the entire video chain from camera to CRT a much easier job. Pictures tend to look sharp. 3MHz or so BW was possible then but not easy. Also 405/50i gave 405 lines only on still pictures. As soon as anything moves the effective vertical resolution drops to 202 lines. This is ignoring aperture effects and Kell factor.
The problem was that 240/25 was really pushing things with mechanical scanning, apart possibly from the telecine. I'm sure Baird himself and BTL (JLB was no longer directly involved by then) that mechanical scanning had run out of steam, hence their work with the Farnsworth "electron camera". Also all receivers except Scophony were fully electronic, again bowing to the inevitable. 240/25 as a standard gave no headroom for improved kit to give better pictures. 405 amply demonstrated that it could benefit from newer technology.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
