Re: filmscanners: LED Illumination for Film Scanners

["Moreno Polloni" <mp@dccnet.com>]

> 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.

All of the parameters of concern can be specifically tailored within the
manufacturing of the LED's, which may or may not be commercially available
standard parts. If you want a high density array, just specify parts that
will provide the illumination level needed.

> 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 do you know how well it could work? Personally, I can't say for sure
because I've never tried it. But I recall the reports from people who tried
the various prototypes to be extremely positive.

> 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.

Whether the light array has gaps or not is of little importance. What
matters is how even the illumination is at the target. You cannot tell how
even the illumination is by looking at the light source itself. You need to
measure it at the target. Whether you're using two, ten, or a hundred LED's
doesn't make a difference, as long as the target is evenly illuminated.

> 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.

Diffusion, if used, can be built into the LED lens, or it can be provided by
supplementary material. I'd assume that in an LED array there would be some
amount of overlap involved to provide even illumination.