RE: filmscanners: LED Illumination for Film Scanners

["Austin Franklin" <darkroom@ix.netcom.com>]

> This isn't much different than a
> contact printing box made up of a dozen or so incandescent lamps
> that can be
> individually switched on or off. In which case you are purposely seeking
> uneven illumination.

It's entirely different.  Incandescent lamps used for such are diffuse and
are not near as focused as LEDs.  Using commercially available standard
parts, you need individual LEDs because you need three colors.  You can only
get the array just so dense, and dense isn't necessarily good.  If you have
too much light, it's too difficult to control.  You don't want to get the
array too close to the film, because that would exaggerate the gaps between
the LEDs.

> I said "dense LED array". The degree of sophistication in that enlarger
> light source was with the control electronics, and high-output LED's with
> very tight spectral parameters. It provided a very precisely controlled,
> low-heat light source that seemed ideal for enlargers.

It's a nice idea, but it fails in the implementation.  It just doesn't work
as well as you may believe it could work.

> How have you determined that the LED's are uneven?

It's a fact that they are uneven.  They have gaps between them, since they
are individual lights, and their housed in plastic that is not very even
optically.  Why don't you just look at the images that were provided with
the light source we've been discussing.  It is blatantly obvious that they
provide uneven illumination.

Of course, you can diffuse them, and you can get them to be more even.  The
problem with that is that you lose some of the supposed "control" you are
touting that they can have, since you are increasing/overlapping the area
each LED covers.  Your tradeoff is evenness of illumination vs control.

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.