[pure-silver] Re: LED light source for enlarger
- From: Sauerwald Mark <mark_sauerwald@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 5 Feb 2009 13:51:44 -0800 (PST)
One issue with using LEDs is the colour spectrum.
'White' LEDs can be made in two different ways - in the first there are three
emitters each with very narrow bands - one at red, one at green and one at
blue. The human eye isn't very good at distinguishing spectral content of
light and we see it as white, but some things look like they have a funny color
under that illumination.
The other type of white LED has a blue emitter, and a phosphor coating which
radiates at lower frequencies when excited by the blue - the result is similar
to a flourescent light, and again, although it looks white to our eyes, it does
not have the same spectral content as a white incandescent bulb.
Another way to build an enlarger head would be to have three different colours
of LEDs and control the intensity of each independently - when doing B&W work,
the question is going to be how well the blue and green line up with the
sensitivity of the paper that you want to use.
I haven't done the research to find out what the spectral sensitivity of the
two emulsions on my preferred (Ilford MGIV FB) paper is. The spectral output
of individual LEDs is fairly narrow as a result of how the light is
generated.
If you wanted to use this head to do color, then you have three LED spectrums
to line up with the different emulsions in color paper.
--- On Thu, 2/5/09, Russ Gorman <rusty57@xxxxxxx> wrote:
From: Russ Gorman <rusty57@xxxxxxx>
Subject: [pure-silver] Re: LED light source for enlarger
To: pure-silver@xxxxxxxxxxxxx
Date: Thursday, February 5, 2009, 4:33 PM
If anyone is interested in trying to make an LED lightsource for their
enlarger, here is a good starting point- a board already custom printed for a
grid of LED's. It's a little large, but gives you an idea of what it
would take and the cost involved (minimal) I'm considering building one for
my 5x7 Zone VI enlarger to replace the coldhead.
Zone VI(Calumet) had designed and built one for this enlarger just before
discontinuing it, so I don't know if they ever sold any- I think it was
$1200 at the time
http://www.evilmadscientist.com/article.php/peggy
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