Question about the Col-R-Tel
 

G'day. I've been trying to get my head around how the Col-R-Tel works considering the fact that there isn't a field for each colour to correspond to the colour wheel like on the CBS Color System. Anyhow reading this article http://www.earlytelevision.org/col-r-tel_article.html brings me to a better understanding of the system and makes me ask this question.

B&W set receiving a colour signal, as I understand the colour signal gets scanned across the B&W screen in the same fashion as on a colour set in a mosaic of dots but as varied greyscale illuminations for each primary colour. Now does the Col-R-Tel basically scan 3 times as fast as a single field hence each each cluster of 3 primary colour dots represented as illumination greyscale dots on the B&W set get hit with the 3 filters (appearing to our eyes) all at once hence appearing as levels of red, blue and green as if hitting a primary colour phosphor dot on a colour set and therefore bringing forth a colour picture? I'm guessing that's how it works but would like to know if this is true or not?

The NTSC signal gets chopped into sequential fields by the converter. R-G-B information is shown on the CRT in turn as each color filter passes in front of the tube. In so doing, the 30 frames per second becomes 10 complete color frames per second with a wheel.

Flicker!

So that means the motion rate of the picture gets divided down by 3 giving a less fluid more jerkier motion picture? Reminds me of those Cartrivision VCRs I read about which used a compression system of recording only every 3rd field http://www.labguysworld.com/Museum017.htm , a demo of this machine in action can be seen here http://www.youtube.com/watch?v=CPEjhiOk2XI on the game show "What's My Line" 1972.

Have to say initially before reading up on the Col-R-Tel article on the Early Television Foundation website I thought the B&W set scanning rate was modified to 180 fields/sec and the NTSC signal gets chopped into sequential fields to reproduce a 30 frame/sec NTSC picture through the wheel. Now that would be a good experiment for technological minded TV enthusiasts to try out hey:thmbsp:

Modifying magnetic scan to 3x rates is VERY difficult if not impossible. It would never be producible as an affordable adapter. Hence the low-frame rate field sequential Colortel.

Sort of. The smoothness of a monochrome image is exactly the same as you are still seeing the same 60 fields per second. On a color image, say a red ball, you only see the image once every 3 fields causing flicker and jerkier motion. Also, because of the 20 color fields/sec, there is always color fringing or breakup. For instance, as a white ball moves across the screen you will see a separate red, blue and green ball, all displaced from each other moving across the screen.

This is not to say a Col-R-Tel cannot produce a very good, perfectly watchable image as shown by Steve in the prior thread.

Darryl

All bullchit. It's actually magic, but we're NOT sposed to let that out...There was a little Wizard that lived in 'em, but after 50 years or so, most of them have retired or moved on.

Ahh, I think I'm starting to understand how it works. So basically you get the full smooth fluid motion 60 fields/sec monochrome image of the colourcast and you get 20 colour fields/sec overlaying the monochrome image hence those colour problems you've mentioned. I guess it works best when there's slower motion and no motion.

Even for gray or white objects there is some flicker because of the different visual brightness of red, blue, and green. Flicker is worst for bright pure green objects, which are both bright and displayed at 20 fields per second.

I will have to see one of these Col-R-Tels in action one day, will be very interesting to see these flickering colour pictures.