DIY LED RGB Complete

[Tin Can]

https://youtu.be/hkdB7-9kuVU

[freesky1992]

https://www.largeformatphotography.i...D+LIGHT+SOURCE
This light source looks also amazing,I am planning to build one for myself.

[Drew Wiley]

But the primary question remains unanswered : how do the RESULTS actually compare to tried and true traditional colorheads using halogen bulbs and dichroic filters? Is there sufficient output for serious scale enlargements, or similar color purity? And how about long-term maintenance issues? I'm skeptical. And if these are simply for VC black and white printing, there's no need for red.

[koraks]

Is there sufficient output for serious scale enlargements, or similar color purity?

The other day I implemented a 4-stop ND filter simulation in my LED head because it was too damn fast. Enlargements of 35mm negative to 8x10" print size at f/8 are around 200 milliseconds without it on my present RGB head. Yes, MILLISECONDS. With the ND filter simulation (which just shifts a 12-bit PWM value a few bits to the right in a 16-bit variable; it's simple really), that becomes a more sensible 3 seconds or so.

Output is not the problem.

[Michael R]

I agree. The LED light source I built for my sensitometer needs a lot of attenuation - actually somewhat more than I had anticipated. And I didn’t even use the most efficient LEDs the company makes because I went overboard/overkill on the emission spectrum.

The other day I implemented a 4-stop ND filter simulation in my LED head because it was too damn fast. Enlargements of 35mm negative to 8x10" print size at f/8 are around 200 milliseconds without it on my present RGB head. Yes, MILLISECONDS. With the ND filter simulation (which just shifts a 12-bit PWM value a few bits to the right in a 16-bit variable; it's simple really), that becomes a more sensible 3 seconds or so.

Output is not the problem.

[Eric Woodbury]

I agree. Extremely bright and annoying to work with. The LED heads I've designed and built have an attenuation knob to reduce output by 1, 2, 3, or 4 stops. Usually it's set to minus 3 stops and the lens to f/11 or f/16. However, the intense light is useful with very dense negatives that would normally be unprintable. I find this offers new opportunities, especially with FP4.

[Drew Wiley]

Output not a problem, Koraks? You've proved nothing. You're talking about a tiny black and white print at f/8. I've punched 30X40 inch Cibachrome prints with registerted .90 density masks in 15 sec with halogen colorheads - in that case, a medium far far slower than either black and white or RA4 papers. Even with my 8x10 format blue-green cold light, I sometimes have to stop the lens down to f/64 to slow down the speed to 10sec, even with a hard blue 47 filter in place for sake of split printing.

And Eric, what keeps "unprintable" FP4 densities unprintable is that they're shouldered off. Maybe masking or some alt UV process could improve that. I recently reprinted some early FP4 negs that once gave me hell; but with current premium VC papers I've had excellent success. They were otherwise overexposed, overdeveloped, and prior to my use of staining pyro developers, which considerably helped highlight repro.

Still doesn't answer my query about color printing use. In that case, you need rather tight spectral performance for good results - and how much light output will that subtract, and what supplementary filtration might be needed? I have no doubt that LED's will work for VC printing. I've sold industrial LED inspection lights so bright they will almost blind a person twenty feet away unless they're wearing welding goggles; but that doesn't mean they're any good for color printing purposes. I certainly not dismissive of the technology; it just seems too adolescent at this point for serious RGB printing work yet.

[koraks]

You're talking about a tiny black and white print at f/8.

COLOR prints. Btw, B&W paper is generally slower than contemporary RA4 paper.

I certainly not dismissive of the technology; it just seems too adolescent at this point for serious RGB printing work yet.

Commercial RA4 exposure systems using RGB LED technology for exposure:
Durst Theta series (although Durst does not manufacture new RA4 exposure equipment as they moved to inkjet)
Epsilon (LED light delivered through fiber optics to printing surface)
Chromira (linear LED bar performing overlapping/staggered exposures)

This is for high-output commercial volume production in operation TODAY as well as over the past 15 years or so. There's nothing 'adolescent' about LED tech for RA4 exposure. It's mature technology in full operational use.

[Tin Can]

Since Drew never shows any evidence

I don't listen


anymore



I did see his website long ago

[Drew Wiley]

koraks - you're talking about extremely expensive platen printing devices which lend a slightly pepperish-grain look if viewed close up. One of my colorhead feedback monitoring devices came from the same folks who made the Chromira; and I've been aware of these as long as they've been around. A big Chromira was in use right across the RR tracks from my office. That was a lot longer than 15 yrs ago. I could have bought it for 10% of its original price when they retired; but I'm not interested in commercial printing; and the printer itself is just one component in a big feed-through system (drum scanner to XY paper roll cutter to printer to big roller transport developer plus dryer, much of it highly expensive to maintain and requiring industrial hazmat permits. People with Lightjets were still having streaking problems back then. Jim Browning, who holds patents on the Chromira, still uses his for making big Durantrans backlit transparencies. But they gave disappointing results with Cibachrome - not enough poop. That's why ZBE also offered their ultra-bright Starlight optical enlarger, which soon fell into disrepute due to the inevitable overheating and short filter life. I had the same problem with my Durst color mural enlarger; and that's why I made my own RGB 8X10 colorhead instead - not only better color, but it ran way cooler.

I don't need to "prove" nuthin' to nobody. Everyone who has ever seen a Chromira print up close knows this, and it's a complaint with high-volume photofinishing LED snapshots too. And none of this has much in common with designing diffused LED heads for sake of optical enlargement. Whole different ballgame. And in that respect, it's very adolescent with respect to proven color printing applications, if even realistic at all except for small prints. The burden of proof isn't upon me - I'm using time tested halogen colorhead technology. But I do wish those mariners well who are trying to cross the ocean for the first time in an LED inflated raft made of translucent diffusion plastic.