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Filmscanners mailing list archive (filmscanners@halftone.co.uk)

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RE: filmscanners: LED Illumination for Film Scanners




> > > A couple of years ago someone on the darkroom newsgroup was working on
> an
> > > LED light source for enlarger heads, utilizing clusters of
> high-intensity
> > > LED's. I don't know what happened to the project, but at the
> time a lot
> of
> > > people were really excited about the technology and the
> initial results
> > > showed a lot of promise.
> > >
> > > http://www.trailing-edge.com/www/led.html
> >
> > Yes, and look at how uneven the lighting is.
>
> Quoting a recent post on this list: "And you can tell this from a
> 72dpi JPEG
> image?"

Not relevant.  Here we are not talking about image quality garnered from a
72PPI image.  Go to the referenced URL above.  Anyone can see that the LEDs
used in that array have very large gaps between them, and the illumination
is VERY uneven...even if it was 10PPI.  Go about halfway down the page.

> > For an enlarger, that may turn
> > out to be a very bad idea, simply because you can't adjust each
> individual
> > LED for even illumination.  At least with a CCD, you can adjust the gain
> for
> > each sensor element to get even illumination.
>
> Why can't you adjust each LED for illumination levels? For instance, the
> designer could quite easily vary the voltage levels throughout
> the array to
> compensate for enlarger lens light fall-off.

Yes, but that's not the issue.

> And taking things one step
> further, a dense LED array positioned closer to the negative could even be
> programmed to provide some degree of selective dodging/burning/variable
> constrast control.

I doubt it.  The control isn't that fine since the array is so course.  Also
it would make the unevenness worse.

> With an appropriate control mechanism, a user could
> adjust for dead even lighting across the easel for a specific lens/format
> size combination.

Not with that array shown, and not without a VERY diffuse diffuser.  Making
an LED array as shown is not a high level of sophistication.  If it truly
worked well, I would believe that it would be being used by the enlarger
manufacturers, or at least offered in the aftermarket.  I don't believe
either is true, or does anyone know differently?

The use of an LED array as a light source for a film enlarger is entirely
different than using an LED array for a scanner, where you have individual
sensors that you can adjust to accommodate for the unevenness of the LEDs.





 




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