Making a VC Cold Light Head?

[Kevin J. Kolosky]

Has anyone here ever made one?

[jon.oman]

Interesting question. I would like to know this as well.

With a cold light head, do you need a set of condensors? Can you get along with just the head, a negative stage, and the lens?

[jeroldharter]

There was a guy selling beseler 8x10 coversion kits with a big spacer and an array of flourescent bulbs. Nowadays, I think LED's might be easier.

[Kevin J. Kolosky]

Yes, but will the LED's work for Variable contrast paper? And how do you control them and make them so that the light is even?

[jon.oman]

There is a thread on using LED's here:

http://www.largeformatphotography.info/forum/showthread.php?68581-LED-Lights-in-an-Enlarger-Head&p=647152&viewfull=1#post647152

[Graybeard]

Has anyone here ever made one?

A color head, such as a Chromega, provides both diffuse illumination and variable contrast (via the color filters). There is the considerable advantage that these use tungsten-halogen projector lamps which continue to be readily available.

If you're working with 4x5, there are plenty of these available. These fit directly onto an Omega (of course) and it should be a simple matter to fit a Chromega to most other enlargers (no condensors are required).

For larger formats, things are not so simple.

[Kevin J. Kolosky]

Here is a homemade one.


78900

[pbryld]

Here is a homemade one.


78900

Did you have the fluorescent tubes custom made?

[Sevo]

Yes, but will the LED's work for Variable contrast paper? And how do you control them and make them so that the light is even?

VC are probably the photographic application best suited for LEDs, as VC paper actually needs the monochromatic light natively delivered by (green and blue) LEDs. The commercial heads I've seen all had very even light, placing the LEDs in a mixed grid of blue and greens, and shining that grid into a secondary mixing box (or sphere) before it enters the enlarger mixing box - such a double mixing setup loses some light, but thanks to the low loss of the monochromatic LEDs, 50W worth of LEDs can be at least as bright as 600W in halogen through filters, so that even a 50% loss at the pre mixing stage leaves the LED head brighter than a conventional one. Controlling the contrast can be done with a dimmer (and dimmable driver) for each LED bank - sophisticated systems use one electronic controller that regulates both banks to a constant exposure at any contrast.

Focusing with blue/green is actually more accurate than with white light, as no chromatic aberration issues with exposure-irrelevant parts of the spectrum will irritate you. If you cannot adequately frame in a blue-green light, you'd need an extra set of white (or red) LEDs for a white (or RGB) framing light.

The most difficult issue actually is cooling the LEDs. 50% photon efficiency rather than less than 5% means that they produce more than a magnitude less heat per photon than halogen, so that heat emission into the path of light is smaller than from the best halogen + cold light filter rigs. But it still means that half the driving power ends in heat - and other than halogen bulbs (which have a working temperature of 800°C) LEDs work best/live longest below 50°C, and will immediately be destroyed somewhere above 120-150°C. So you need a fairly sophisticated cooling system to keep 50W worth of tightly packed LEDs in the safe temperature range.

[Kevin J. Kolosky]

"So you need a fairly sophisticated cooling system to keep 50W worth of tightly packed LEDs in the safe temperature range."

Which is why I think most photographers, if interested, would prefer to make a cold light VC head.

I wonder how much the Chromatic abberation has an effect on sharpness in printing. I know Peak sells a focuser that comes with a filter to help with that issue, but the price is quite steep. Still, lots of good photographers over the years have been able to make some pretty sharp prints without all of those fancy things.

I know one needs two tubes, one for Green (Low contrast) and the other Blue( high contrast). I know you place the B. tube above the G. tube in such a way that it looks like G.B.G.B.G.B..... when looked at from the bottom. I know you can use one transformer (60-80W) to power the both tubes, but the tubes must be switched on sequentially. You can buy a toggle switch at a Radio Shack. When it is standing up, it's OFF, when you flip it to right(BLUE) or left(GREEN), it's ON. I know you control contrast by exposing G.B. sequentially. And I know that a cold light does not generate heat so you could make the box with plywood, or you can have a sheet metal guy make one for you.

What I don't know is how you get the tubes bent, or which tubes to buy, and where to buy them.

[Sevo]

I know one needs two tubes, one for Green (Low contrast) and the other Blue( high contrast). I know you place the B. tube above the G. tube in such a way that it looks like G.B.G.B.G.B..... when looked at from the bottom. I know you can use one transformer (60-80W) to power the both tubes, but the tubes must be switched on sequentially.

The ugly thing about tubes is their extremely inconsistent light output during warmup cycles. And that will get even worse if you operate two tubes at different dimmer settings. Serious tube light heads are permanently burning and use shutters for exposure, but that is a requirement that does not really mix well with "affordable" DIY.

Besides, "cold lights" generate quite significant amounts of heat - about half way between LEDs and halogen. The tubes themselves have no issue with a heat buildup to maybe 200°C (at which point their plastics components will start to decompose), but they grow hot enough that the head design has to account for that.

[Mark Sampson]

Zone VI made a variable-contrast cold-light head, and I believe Ilford also offered one- the Multigrade head? Fred Picker mentioned in his newsletters another one called the "Codelight" that was out of production by the '70s, he thought of it as the holy grail of enlarger light sources at the time. I've never used any of them, don't know how popular they are/were, but they are out there if you want to search. Might save some engineering time that way.

[Heroique]

Has anyone here ever made one?

People w/ D2-series enlargers have an inexpensive way to do this.

All you need is an Omegalite (diffusion) head – not so difficult to find, but getting more so w/ time.

If you have one, replace your condenser (or variable condenser) head & lamp house w/ the Omegalite head, and use GE’s “Circline” tube (below). A perfect fit. The tube emits a warm, natural light, making it easy to use w/ multicontrast papers. I think GE calls it “kitchen & bath 22” and the product number is 11084. Most hardware stores should carry it in the $7-10 range.

-----
BTW, this should work for D-II, D-2, D-3, D-5, D-6 series enlargers (but not the D4).

[Graybeard]

People with D2-series enlargers have an inexpensive way to do this.

All you need is an Omegalite (diffusion) head – not so difficult to find, but getting more so w/ time.

If you have one, replace your condenser (or variable condenser) head & lamp house w/ the Omegalite head, and use GE’s “Circline” tube (below). A perfect fit. The tube emits a warm, natural light, making it easy to use w/ multicontrast papers. I think GE calls it “kitchen & bath 22” and the product number is 11084. Most hardware stores should carry it in the $7-10 range.

Walmart carries these tubes.

I believe that there is also a 5x7 version of the Omegalite head.

[Kevin J. Kolosky]

"Zone VI made a variable-contrast cold-light head"

I am aware of this. They took $150 worth of parts and dolled it all up and painted it up fancy and sold it for $700.00 (which is fine, everybody needs to eat), and since they aren't being manufactured anymore they are still $700.00!!! I have one of their regular cold light heads and it is a fine piece of equipment, but you have to stock 3 different grades of paper if you want to have any contrast control when printing!

[Keith Fleming]

It is still possible to buy new Aristo VC cold-light heads. See at www.light-sources.com.

Keith

[Charlie Strack]

It is still possible to buy new Aristo VC cold-light heads. See at www.light-sources.com.

Keith

It is possible to buy Aristo REPLACEMENT tubes--I don't believe Light Sources is manufacturing complete heads.

Charlie

[Curt]

It is possible to buy Aristo REPLACEMENT tubes--I don't believe Light Sources is manufacturing complete heads.

Charlie

That's correct. Just a small list of the most commonly asked for TUBES. Nothing else.

[Sal Santamaura]

...Nowadays, I think LED's might be easier.I doubt it would be easier if making one's own, but the technology can certainly be superior. I have one of these


http://heilandelectronic.de/led_kaltlicht

which is adapted to a Beseler 23CIII. Even though that's a 6x9 enlarger, Herr Heiland used one of his 4x5 light sources. Clearances and configuration of the Beseler's upper stage are such that a 6x9 source cannot be close enough to the negative for complete coverage, so the larger source was necessary. Upside is that, when I eventually have a permanent darkroom with enough space for a 4x5 enlarger, the led light source will be usable on it too.

I use this Heiland led source / Beseler enlarger both for enlarging roll film negatives and to contact print large format negatives. It has a finned aluminum heat sink on top of the led array (purely passive cooling) that never gets more than slightly warm during use. Both exposure time and contrast are adjustable in 0.1 increments. There's no drift between exposures. I'm completely satisfied. About the only thing that could make me happier would have been a better dollar/euro exchange rate when it was purchased around four years ago. :)

[jon.oman]

I doubt it would be easier if making one's own, but the technology can certainly be superior. I have one of these


http://heilandelectronic.de/led_kaltlicht

which is adapted to a Beseler 23CIII. Even though that's a 6x9 enlarger, Herr Heiland used one of his 4x5 light sources. Clearances and configuration of the Beseler's upper stage are such that a 6x9 source cannot be close enough to the negative for complete coverage, so the larger source was necessary. Upside is that, when I eventually have a permanent darkroom with enough space for a 4x5 enlarger, the led light source will be usable on it too.

I use this Heiland led source / Beseler enlarger both for enlarging roll film negatives and to contact print large format negatives. It has a finned aluminum heat sink on top of the led array (purely passive cooling) that never gets more than slightly warm during use. Both exposure time and contrast are adjustable in 0.1 increments. There's no drift between exposures. I'm completely satisfied. About the only thing that could make me happier would have been a better dollar/euro exchange rate when it was purchased around four years ago. :)

This looks great! Here is a link to the English version: http://heilandelectronic.de/led_kaltlicht/lang:en

I don't see any prices, what did you pay for your 4x5 version?

[Sal Santamaura]

This looks great! Here is a link to the English version: http://heilandelectronic.de/led_kaltlicht/lang:en...Thanks for the updated link. I'd clicked on the "English" flag to read it before posting, which must have left a cookie on my computer, since even my original link comes up in English here.


...I don't see any prices, what did you pay for your 4x5 version?Since that was quite some time ago (exchange rates are different now) and the job involved a lot of custom adaptation to the 23CIII, it would be better to simply email Heiland for a price. Let's just say it wasn't inexpensive. :)