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RE: filmscanners: LED Illumination for Film Scanners



> > LEDs have been around for a very long time, and they are reasonably
> > inexpensive, as well as very easy to control.  I am sure that
> if this was
> > such a great idea, and the implementation worked near as well as you
> > believe, it would have been done some 15-20 years ago as a commercial
> > venture, but, alas, it wasn't.
>
>
> An LED light source for enlargers was not done 15-20 years ago because it
> was not possible. Blue LED's did not exist as anything other than
> laboratory
> curiosities until within the last 5 years.

Sure you could have done that 15-20 years ago.  Use filters...red, green and
blue filters certainly were around 15-20 years ago.

> With the current decline of chemical imaging such a
> source would possibly not be commercially viable, but it is technically
> feasible.

Possibly, but it really depends on what you mean by technically feasible.
What are your design goals?  The discussion was a controllable LED light
source, and I still contend that is not really as feasible as "the
discussion" was claiming it was.  Of course you can make an LED light source
that will evenly illuminate, but that was not the design goal being
discussed.

They are also harder TO control evenness, since there are so many different
lamps...and they do have tolerances, and unlike the scanner, you can't
adjust the input values of the individual sensors to make up for this
unevenness.  That is, unless you wanted to go through some exhaustive
calibration process.  I don't know how much these drift, but they may have
the need to be re-calibrated in the field.  Also, remember scanners are only
one dimensional, an enlarger is two dimensional.

> As far as the uneven character of the source shown at
> http://www.trailing-edge.com/www/led.html , it's no worse than the three
> lamp sources found in RGB color heads in some additive enlargers. The
> individual bulbs used there are spaced a couple of inches apart and yet
> their light is mixed to provide an even, color controlled source.

But the "tout" for using LEDs is that they can be individually controlled,
which they, of course, can be, but the problem is the more you diffuse them,
the less area control you have.




 




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