Hi Klass
I understand all your comments about the attenuation of film, and the low contrast ratio ensuing. I have an immediate comeback to those comments. Simply pasting TWO (or three!) of the films back to back would immediately significantly increase the contrast, no? If one wishes, instead of a clear area, the ‘holes’ could be actual holes in the film, introducing no additional attenuation in that area. This multiple film idea would also significantly strengthen the film itself for fast traversal through the mechanism.
One could also go to the effort of painting the film by hand, masking the black areas with some reflective silver paint, for example, further reducing attenuation and (?) also increasing the light available to the holes, if the LED array was backed by a mirror and the silver back to the film managed to reflect light back into the LED ‘box’.
Another idea I’m not so keen about is that the columns of the LED array could also be turned off when not needed (that is, say there were 4 columns of LEDs, then the first is only turned on when scanning the first (say) 10 or so scanlines, the second is turned on only when we scan lines (say) 8-18, etc – a bit of overlap there is intentional. I’m not so keen on this because I’m still rather uncomfortable using a LED system in the first place; it feels like cheating… so using the advantages a LED array has to offer is cheating even more. One could simulate this by having a secondary belt that ran perpendicular to the first, the belt only allowing light through for the scanline being drawn. This would reduce the light through the black area by 32x, of course.
To be honest, I’m not particularly interested in film wear – I have more interest in if such a system could be made to show a good picture (even if parts have to be replaced once a week, that’s OK!). Mind you, I’m nowhere near actually making this yet, this is just a ‘what if’ at the moment.
Cheers
A
Klaas Robers wrote:The idea of the film-loop monitor is very old. Drawings were published long ago. But there is a not so simple to see problem that prevents us from using it.
First the film has to pass the sprocket wheels so frequently that it will wear out very fast. Film and sprocket wheels are not designed to run so fast, it will be running 400 frames per second. Then the speeds and the forces are too large to be handled by the rather fragile plasic of the film.
However this can be overcome by glueing the loop in a circle onto a disc and producing a drum monitor.
But there is another problem that I will try to point out for you.
1. Suppose we have a system with 32 lines and 32 dots per line. In total this is 1000 dots per frame.
2. One frame has a transparent dot with a surface of 1/1000 of the total frame.
3. So 99,9% of the frame is black.
4. So we throw away 99,9% of the light en keep only 0,1%.
This explains why we need so much light and still remain a rather dim picture.
I use 32 high brightness LED's at 50 mA peak current. You can't look into that.
5. Each dot of the picture is illuminated by this light 0,1% of the time through the "hole" of the disc.
6. If you use film this is attenuated by the transparency of the hole, say 0,9.
7. So this gives an illumination of 0,09% of the brightness of the LED-array. Still about 0,1%.
8. But each dot of the picture is also illuminated in the remaining 99,9% of the time
9. This is attenuated by the darkness of the film.
10. Suppose the attenuation of the film is 500 x. This is already very good for silver halide film.
11. Then each dot is illuminated as well with 0,2% of the light of the array during the other dots.
12. Say that the light is on for 50% of the dots,
13. Then this stray-illumination is 0,1%, the same as the illumination through the "hole".
14. So white dots get an illumination of 0,2%,
15. and black dots an illumination of 0,1%.
16. The so called contrast ratio is 1 : 2, which is extremely poor.
I know that a contrast of 1:500 can be reached by Black and White (silver halide) film. There is also special graphical material that can do only total black and total white, no gray shades. I don't know its contrast ratio, may be it is somewhat better. But if we want to come to 1:100 we need an improvement of a factor of 50 x. I doubt this. Besides this material will only be available as sheets, not as 35mm film. There is no need for graphical material in the movie industry.......