RE: filmscanners: LED Illumination for Enlargers

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

> > 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.

Do you have any idea where those reports are?

> > 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.

I believe you're either missing a very important point.  Each LEDs output
has tolerances.  Since the are more point light sources than not, and you
have many of them, they will NOT provide even illumination for each
individual LED, and diffusing them will not solve this.  You would have to
calibrate them over the entire array projection area, and for most every
magnification you would use...which I believe is an ominous task, and not
conducive to field calibration either.

> > 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.

I do not believe diffusing the single LEDs does near as well as diffusing
the entire array.

I've given you my engineering evaluation of it, and you haven't shown
(certainly not to my satisfaction anyway) that my concerns aren't valid.
You seem to really want this to work!  I don't believe we're getting
anywhere here, though I did learn about the origin of blue LEDs, and this is
really off the topic of film scanners at this point.