DIY light source for 10X10" enlarger.

jjs wrote:
In return for the good input (and in the original spirit of Usenet) I will
look into the LED array simply to get a realistic idea of what it would cost
for enough light, what the proper power supply would cost, and try to get
the actual color temp of so-called white LEDs and post back. It will take a
while.

http://www.elektor.com/magazines/200...s.350167.lynkx

You have to pay for the article, but the free description has some links to
manufacturer's web sites.

Finally, I must test the electric shutter on B for a few minutes. It was not
used that way in its original camera, but I have a fused box on the bench
and welding gloves.

It does not have to be a very sophisticated shutter, a solenoid with
a spring return, or a 1/2 turn stepper motor would do. We are not
looking for exposure accuracy here, the electronics will handle
that (even if it is a pushbutton switch and you control it).

Remember that a 1% variation in exposure is not going to be noticable,
and that could easily be 1/2 second. It depends upon how much straight
printing you want to do versus dodging and burning. :-)


Tonight I will try to find time to do tentative drawings of a couple
housings - one for traditional incandescents, and one for the external
lights idea.

Good luck.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

In article ,
jjs jjs.jjs.net wrote:
This has been a terrific thread of brainstorming. I've learned a lot and
also got pointers to things to explore further.

In return for the good input (and in the original spirit of Usenet) I will
look into the LED array simply to get a realistic idea of what it would cost
for enough light, what the proper power supply would cost, and try to get
the actual color temp of so-called white LEDs and post back. It will take a
while.

"White" LEDs don't have a color temperature; they are not blackbody light
sources. You're going to have the same problems you would with a fluorescent
lamp, color-wise...

--
Thor Lancelot Simon

"The inconsistency is startling, though admittedly, if consistency is to
be abandoned or transcended, there is no problem." - Noam Chomsky

In article ,
Richard Knoppow wrote:

Cold light lamps are just fluorescent lamps. I think you

Yes and no -- they've got a somewhat unusual spectrum and they have
special ballasts and a large preheater. The latter two differences
from your run of the mill fluorescent lamp are meant to make them
more useful for enlarging by reducing the warm up time that causes
problems for short exposures.

These are worthwhile differences but with an enlarging timer that
measures light output, like the Metrolux, much less so.

--
Thor Lancelot Simon

"The inconsistency is startling, though admittedly, if consistency is to
be abandoned or transcended, there is no problem." - Noam Chomsky

Thor Lancelot Simon wrote:

"White" LEDs don't have a color temperature; they are not blackbody light
sources. You're going to have the same problems you would with a
fluorescent lamp, color-wise...


I did see an article somewhere for an enlarger head using LED's but a mix of
I think blue and green were used*, their output or exposure times were
variable to give a multigrade head.

*Seems an odd choice to me but the chap knows more than I do.

Pete

--
http://www.petezilla.co.uk

On Wed, 09 Apr 2008 10:43:19 -0700, David Nebenzahl wrote:

On 4/9/2008 10:19 AM Geoffrey S. Mendelson spake thus:

As for incandescent bulbs, you may have to find ones with the lettering
on the side instead of the bottom.

There are ways to remove the lettering on the bottom. (Don't ask me how
I know that.)

Use acetone. Fingernail polish remover will do--It's mostly acetone--but
you'll need to use isopropyl alcohol (NOT rubbing alcohol--it contains
oil) after to remove the additives in the polish remover left on the bulb
that keep the nails from becoming dry and brittle.

Stef

"Thor Lancelot Simon" wrote in message
...
In article
,
Richard Knoppow wrote:

Cold light lamps are just fluorescent lamps. I think
you

Yes and no -- they've got a somewhat unusual spectrum and
they have
special ballasts and a large preheater. The latter two
differences
from your run of the mill fluorescent lamp are meant to
make them
more useful for enlarging by reducing the warm up time
that causes
problems for short exposures.

These are worthwhile differences but with an enlarging
timer that
measures light output, like the Metrolux, much less so.

--
Thor Lancelot Simon


Not all cold light heads have the heaters. They are
mostly on Arista lamphouses and are meant to maintain the
light output of the lamp when not run continuously. The
phosphors may be different but there are at least two types
of lamp offered by Arista, one being balanced better for VC
paper. One can buy several types of flourescent lamps
including at least one phosphor with a visual color similar
to incandescent lamps. The spectral outputs for the
phosphors are available from most lamp manufactuers so its
possible to see if the spectra is suitable for VC paper.
I have no idea of what differences there are in the
balasts other than to withstand intermittent operation.
All gaseous discharge lamps have outputs which increase
with temperature so they like to run hot. In a diy lamphouse
the only method of getting consitent light output is to run
the thing continuously and use a shutter to control the
exposure.


--
---
Richard Knoppow
Los Angeles, CA, USA

"gr" wrote in message
...
jjs wrote:
To date I've considered enlarger light sources to be
engineering well beyond my feeble capability, but I have
used and examined only condenser enlargers such as the
Leitz IIa and Omega condenser enlarger, but my task now
is to make a diffusion thpe for the 10x10 enlarger.

I want something with No built-in filtration. No fancy
color mixing for VC papers. No electronics. No side-lit
mixing chambers. Just a straight forward light source and
a diffusing layer. I question cold light, mercury vapor,
tubes, whatever they are because I just don't plain
understand 'em.

I can blunder head-first into this project, but this
group has some smart people with impressive experience,
so I'll put my blunder idea forward.

First, I am limited to ~110V AC power although converting
to DC is an option. How about a simple array of 'white'
LEDs at the top, pointing down over the typical sheet of
plastic translucent material found in home supply places?
Or should it be fine ground glass? I am not concerned
about the variability of LEDs over time unless they
change during the time it takes to get an 8X10
negative-to-print just right - maybe a day or two. The
power for the light will be run through a robust
power-conditioner once set aside for a big minicomputer.
Batteries not included.

So far so good? Corrections would be most welcome. OR
just let me blunder and if it goes badly I'll post
pictures of the catastrophe.


Forget florescent lamps unless you run then continuous and
use a shutter; even then they can vary intensity quite a
bit. Tubes have a warm up vs output curve of 30 minutes or
so, CF type take at least 5 min to come up close to full
output. An integrator would allow use.

If I was making a quick light box for an 8x10 enlarger, I
would use multiple bulbs (4 or 6) (prob small qz halogen
to distribute the light more evenly and then 2 white plex
diffusers spaced 1-2" apart between the bulb and the neg.
gr

The problem with incandescent lamps is heat. Dissipating
the heat will make construction of the housing more complex.
If one uses an enlarging meter the variations of flourescent
lamps with temperature is of much less importance. Even
though flourescent lamps like to run hot the heat involved
is still much less than it would be for incandescent lamps
of similar output.


--
---
Richard Knoppow
Los Angeles, CA, USA

Nicholas O. Lindan wrote:
Ilford MGIV paper is a 3-emulsion paper, the third emulsion
sensitized for cyan. For best control - especially at low
contrast grades - the head would also have cyan LEDs.

I've never heard of cyan LEDs. Green and blue will look cyan to the
eye, but I have no idea if it will activate that layer, my guess is
not.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

On Wed, 09 Apr 2008 12:11:47 -0500, jjs wrote:

"Thor Lancelot Simon" wrote in message
...

A fluorescent light source of some kind -- a "cold light" source --
will give you the most light for the least power (and heat) unless you
really want to use a *lot* of white LEDs. I'm not sure you can get
enough output from a 10x10 grid of LEDs you assemble yourself to give
decent enlarging times with a 10x10 negative, and I am also skeptical
that it will be as even as you'd get with an array of fluorescent
tubes.

This is great, Thor. I appreciate your input.

Are these flourescent sources in round tubes? Or would it be a line of
short tubes? And I gather that they would be left on all the time and
I'd use the lens shutter, correct?

JJS,

IIRC, one of the Ansel Adams Photo Series books from years ago had
detailed instructions on how Adams built a diffusion head light source
for a horizontal enlarger made from a salvaged 8x10 camera. It used an
array of small incandescent bulbs, opal glass for diffusion, and a vacuum
cleaner for heat removal. Very simple.

I adapted the design to a vertical 4x5 enlarger, using below-the-lens VC
filters. Worked quite well, but when I could afford it, I replaced it
with an Aristo head color balanced for VC paper.

Stef

"Peter Chant" wrote

enlarger head using LED's but a mix of
I think blue and green were used ... Seems an odd choice to me

Blue and green are correct. Both emulsions are sensitive to
blue light and one of the emulsions is sensitized so it will
also respond to green light.

The multi-contrast gel filters add red light for better visibility
when dodging and burning -
red + blue = magenta
red + green = yellow

A proper head would have red, green and blue LEDs - allowing
it to produce 'white' light for focusing and graded paper,
magenta and yellow light for VC paper, and red light for
positioning sensitive materials.

Ilford MGIV paper is a 3-emulsion paper, the third emulsion
sensitized for cyan. For best control - especially at low
contrast grades - the head would also have cyan LEDs.

--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index2.htm
n o lindan at ix dot netcom dot com