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Old 31st Dec 2006, 1:03 pm   #1
Panrock
Octode
 
Join Date: Feb 2005
Location: Sedgeberrow, Worcestershire. UK.
Posts: 1,460
Default Colour mixing in mechanical television

Quote:
Originally Posted by tubesrule View Post
Sure thing Steve. The main page is here: http://www.earlytelevision.org/color...w.html#12-21aI am very anxious to see what kind of results Steve M. gets from this project. The 30 line mirror screw sets I've seen operating are very impressive.Darryl
Quote:
Originally Posted by Panrock View Post
I'd have probably not tried to persuade light from LEDs into optical fibres like Steve McVoy did, but would have tried a different approach, namely having a stack of narrow-angle ultra-brights some distance behind a vertical slit (probably bearing a perspex/frosted 'mixing rod') at the end of a light box, with the LEDs adjusted to beam toward the slit and mixing there. I would have thought this would be more efficient and give a brighter picture. It's a variation on the arrangement I currently use. Steve
Quote:
Originally Posted by Steve_McVoy View Post
Steve - I'd like some more details of the arrangement you use for your mechanical light source, and in particular of the perspex/frosted 'mixing rod'. It may well be a better solution than the fiber optic one.
Steve, the method you have adopted to mix the colours for your 60-line mirror-screw monitor looks superbly engineered as always, and I offer my own suggestions with due respect. My idea would not be perfectly efficient either, but I think it might be more so.

The problem is how to efficiently concentrate the modulated light from your super-bright coloured LEDs onto the long narrow slit (necessary for illuminating mirror-screw displays) and also how to effectively mix the light from the three coloured primaries.

As I see it, the key to the solution is to exploit the narrow angle beams of your LEDs (typically only 15). This means that almost all their light will be concentrated in a patch 3 times smaller across than the distance from the LEDs (1/tanθ). So my colour light mixing box consisted of a mosaic of red green and blue LEDs at one end of quite a long box, with a ground glass screen at the other end. This is an efficient arrangement. Using 15 LEDs the box should be about 3 times longer than it was wide; then virtually all the light from the coloured LEDs would then arrive on the screen and be thoroughly mixed.

The problem then becomes how to adapt this arrangement to concentrate the light to mix on a narrow slit, rather than a broad square. I therefore think the LEDs should be arrayed in RGB sequence along a line rather than as a mosaic (in my case), set some way back from the exit slit. Their natural beam overlap should provide effective colour mixing at the exit slit.

In passing, I see that 8 super-brights are available in the Maplin catalogue (UK). So then the light would spread out 7 times less than the distance it is from the LED. Basically, the tighter the LED beams - the better...

But still, a lot of the light will get lost where it misses the narrow exit slit. If two reflective plates were added either side of the diverging beam, positioned half way between the slit and the LEDs, then more of the light should emerge from the slit (and then diverge again). Using parallel reflective plates, the natural divergence angle of your LEDs then becomes the viewing angle.

On further reflection, I think a perspex rod placed just behind the exit slit might collect more light but it would also act as a strong diverging lens. This might only become worthwhile if the viewing angle were otherwise too narrow.

Steve, I emphasise I am thinking off the cuff here so my ideas may well have drawbacks I haven't yet thought of!! I tend to just go ahead and try things out to see what happens in practice, rather than plan properly beforehand!

Anyway, I think your existing plans are already well thought-out and will give very impressive results.

Steve
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