Build my own color head?

Drew, I am somewhat puzzled by your insisting on halogen heads being brighter than LEDs. Just to be clear, I have no experience with color printing, but based on simple physics your statement seems implausible. For example, start with 1000W electrical power:

Halogen: 1000W electrical -> 200W light -> filtering (3 20 nm bands out of ~300nm visible spectrum, 20% makes it through) -> 40W available light
LED: 1000W electrical-> 400W light -> no filtering since it is emitted in 20nm bands -> 400W available light

Or conversely, 100W of LED would equal 1000W of halogen. Of course, this is a very rough estimate and may have missed various factors of 2, but even then the advantage seems to be with the LED. What am I missing here?

btaylor said:

I have purchased multiple working color heads for my Beseler 45 for under $100 in the last couple of years. I would think a DIY conversion with ordinary hardware store stuff wouldn’t be terribly difficult. My 2 cents worth.

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Actually, there was once an adapter made to mount a Beseler color head on a D2/D2V. I used a dichro 45S on my D2V about 20-25 years ago. I wish I could remember who made it...

eddie said:

Actually, there was once an adapter made to mount a Beseler color head on a D2/D2V. I used a dichro 45S on my D2V about 20-25 years ago. I wish I could remember who made it...

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Please! Availability of one of those would double my search space for a color head for my D2V.

I've been searching for the information. Unfortunately, the only reference I found was a post, here, from PE. I'll keep looking, but you might want to ask khb and Glennview. If I come across anything, I'll be sure to let you know.

Right now LED blows Halogen away power wise and you don't dump 95% of your power as waste heat. My LED head (B&W only) is 4 stops brighter than the stock Beseler head at full power using 35.5 watts and the illumination is more even. No need for IR blocking glass or fans and I'm not cooking filters.

Incandescent Colorheads with their gears and filters are like wooden wagon wheels in a modern age. They have reached the top of their game. The major issues have been solved and the product it good but nobody is building more when steel wheels are better/cheaper.

The motivation for me was the lack of affordable diffusion sources. Cold Light is unstable and parts unavailable. Ilford heads are rare and out of production. The LEDs are VERY stable, much more so than incandescent running from wall power and there is less less heat and power wasted in blocking light (filters).

I am happy with my build and encourage others. You never know what you will find. I didn't know about split contrast printing before I started the project and now I have a whole new tool.

A total misunderstanding here. You are not comparing apples to apples. Once you narrow or trim down the output of LED's to ideal spectral performance with the necessary added dense filtration, there goes much of your light. A color accurate source is quite a bit more challenging project than just a VC project. And as far as potential output, I've used halogen colorheads ten times brighter than a basic Beseler version. There is also the consideration of maintenance over time. Bulbs for most pro halogen colorheads haven't changed for the past 50 yrs. But with rapidly evolving LED technology, you've got the same risk as digital workflow - all kinds of things go obsolete in just a few years. You might call crocodiles and turtles old-fashioned too, but they outlived the age of dinosaurs!

Light loss should be less through cutoff filters with a narrow band LED than a broad spectrum Halogen.

Halogen bulbs are consumables, LEDs not so much. LEDs have such a long life that many LED lighting fixtures make no provision to change the "bulb". That said I have spares in case I mess something up.

I agree, a colorhead is a much more ambitious project than VC but progress has been made and there is a lot of potential.

Halogen bulbs could be made illegal by the same do gooders who outlawed other tungsten bulbs. Watch out!

I have a D3, standard condenser head and an Omega Cold Light, when I printed color I used the condenser head with filters, I have a set of Unicolor filters as well as Kodak Color Correction filters, with a Omega color analyser I was able to print color with no large issues. While in the Air Force I used D5s with color head, and at a newspaper I worked for a while a Beseler 23c with a color head, the only difference between a color head and filters is that a color head being diffusion dust doesnt up as easy, and a condenser head has some what more contrast. I now have a LPL 6700 with color head, no difference in quality, a lot more convenient to change the filter pack, still once I get the filters right on the D3 I can print a box of 100 sheets without fussing too much with filter pack.

With tungsten halogen light, like sunlight, you have a continuous "black body" spectrum, though skewed toward the warm end. There is no such thing with LED. The lights can be mixed to simulate a continuous spectrum and try to fool the eye, which helps for architectural or display applications, but that doesn't mean all three of the spectral peaks which need to be hit will be. There is a similar problem with fluorescent lighting, including cold lights. When you speak of narrow band LED's, just how narrow are they?, and how are you going to trim the unwanted part of the spectrum off if they're not ideal? The concept is fine, but I'm rather skeptical that the correct components even exist quite yet. They are probably coming, but when? Films and papers are engineered for very specific nm points of light. Miss centering on those peaks and you're going to have compromised color reproduction. I realize that all kinds of things can nominally produce color prints; but if you expect high quality hue reproduction, that is a completely different story. For example, once in awhile I've printed the same 4x5 chrome image with both an ordinary Chromega YMC colorhead and my custom additive RGB halogen unit, and the difference is significant in terms of the greater saturation, contrast, and hue purity of the latter. That doesn't necessarily make it any more artistically valid one way or the other; but there is an obvious technical improvement. As far a gel filter packs go, besides their inconvenience, I would want continuously adjustable filtration within 1CC. And yes, my color vision is trained well enough to see those kind of increments in print once fine-tuning the image is in question. A 5cc option would be like a fly ball over the left fence. Some of these newer CN films like Ektar are rather contrasty and respond to changes rather quickly.

I have toyed with this idea as well, but not seriously enough to undertake a project. However, I think it is feasible.

A quick question. Do you intend your color head for black and white printing or color printing? You might have mentioned it, but if so I missed it.

I found what purports to be a graph of spectral sensitivity curves for Kodak Endura paper. (figure attached) I suspect that other color papers will be similar.

From those curves it looks to me like you would want to select RGB LEDs with peak wavelengths approximately 700nm for red, 550nm for green and 450nm for blue, though there is probably some wiggle room in those numbers, especially on the red side (e.g. 650nm).

You can look at LEDs for sale on ebay. A lot of them list their peak wavelengths, and I believe some list the emission spectral distributions as well.

alanrockwood said:

You can look at LEDs for sale on ebay. A lot of them list their peak wavelengths, and I believe some list the emission spectral distributions as well.

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That's what I did, comparing them with the graphs like you posted which are provided in the datasheets of both endura and chrystal archive papers. They're quite similar.

All of this is now moot, as far as I'm concerned -- I found a deal I could afford on a D2 with Chomega II head (likely less than I'd have spent building an LED color head, regardless how will it would or wouldn't have worked -- and this one month, of all months, I had the money to spend it all at once), and it's now at my home waiting for the darkroom space to be ready for it. I've also gotten a replacement condenser head to replace the cold light for my D2V, in which I can use VC filters in the condenser housing (rather than under the lens), so I'll have a two-enlarger darkroom when it's all in place.

Just to check up -- I recall hearing/reading there is a safelight that can be used with RA-4 materials, and I see from those spectral curves posted above that it looks like that would be a narrow band emission at appr. 575nm -- which is on the yellow side of the the human eye overall sensitivity maximum and also a little redder than the yellow sodium line used in sodium vapor safelights. I see it as down about -1.45+ on the log sensitivity vertical axis -- am I correct in thinking that's just less than a full stop less sensitive than the magenta-forming peak, which is to say, such a safelight would have to be exceedingly dim? Still, it would be better than total darkness for ensuring paper is emulsion up and correctly positioned on the easel, etc.

Sounds great, nice having a 2 enlarger set up, I don't have room for 2 4X5s, I get along with my D3 and a 6X7

Donald Qualls said:

Just to check up -- I recall hearing/reading there is a safelight that can be used with RA-4 materials, and I see from those spectral curves posted above that it looks like that would be a narrow band emission at appr. 575nm -- which is on the yellow side of the the human eye overall sensitivity maximum and also a little redder than the yellow sodium line used in sodium vapor safelights. I see it as down about -1.45+ on the log sensitivity vertical axis -- am I correct in thinking that's just less than a full stop less sensitive than the magenta-forming peak, which is to say, such a safelight would have to be exceedingly dim? Still, it would be better than total darkness for ensuring paper is emulsion up and correctly positioned on the easel, etc.

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It might be useful to post this question in a new thread in the Colour Film, Paper and Chemistry sub-forum, where a few more of the colour darkroom people tend to hang out: https://www.photrio.com/forum/forums/color-film-paper-and-chemistry.86/

MattKing said:

It might be useful to post this question in a new thread in the Colour Film, Paper and Chemistry sub-forum, where a few more of the colour darkroom people tend to hang out: https://www.photrio.com/forum/forums/color-film-paper-and-chemistry.86/

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I'll be over there in a little bit anyway, I'll go ahead and post this over there.