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Re: filmscanners: exposing C41 for scanning ( was gibberish

On Sat, 30 Jun 2001 07:26:58 -0400  rafeb (rafeb@channel1.com) wrote:

> I'm hoping (without evidence) that you're mistaken about 
> the swiveling LEDs.  A 645 negative is approximately 
> 7,000 scan lines along the length of the strip (4.5 cm, 
> at 4000 dpi) and that would mean 21,000 mechanical 
> motions of the LED array (or 28,000 if you add the IR 
> channel.)
> I much prefer to believe they're switching the illuminant 
> colors electronically.

Rafe, please don't take what I said as gospel - I'm relying on my raddled 
memory of a description I saw of the LS1000 mechanism many years ago, and 
may well have it *completely* wrong.

What I *think* I recall is that the LED array is both switched 
electronically and moved mechanically at each scan line position, so the 
successive R, G & B exposures are made with R, G & B LED's and monochrome 
strip sensor 'looking at' precisely the same strip of film image 1 pixel 
high. IOW the LED array is positioned differently for each channel 
exposure, the relevant LED's turned on for the exposure duration, and then 
the cycle repeated for the next scan line, and so on.

This makes a certain amount of sense

    R |
    G | |CCD
    B |

would obviously give unequal path lengths, and involve oblique exposures 
through different bits of film

my recollection is

        R  |
  pivot oG | |CCD  (in this position G is on, R & B are off)
        B  |
 pivot o R | |CCD  (now R is on, G & B are off)
        G  |
and so on...

Regarding Ed's later comments, especially regarding the solidly mounted 
LED, there are two possible explanations (i)I am losing the plot - 
not unlikely (ii)they now move the CCD instead!


Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner 
info & comparisons


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