Are CC values linear?

[AgX]

Wouldn't just buying that 35mm Philips additive enlarger with incandescant lighting yield an outcome?

Bumb...

(Actually there were two different enlargers. The older, substractive model accepts a special additive head.)

 

[Rudeofus]

If I look at the spectral curves from Mr. Bill's link, these are highly uneven spectra even within their range. Now add to that the (probably also) uneven spectrum of color negative film and the fact that not all emulsions (and therefore spectral properties) from different manufacturers are created equal, and that small variations in fixer pH can shift dye hues.

Suddenly a color head based on these narrow band LEDs sounds quite finicky, which seems to be confirmed by Drew's experiences. It might be necessary to use a range of LEDs for each color, each at a slightly different wave length around the spectral maxima of the photographic paper.

 

[Chan Tran]

Bettersense go ahead and build it! It would be a great thing. Enlarger manufacturers don't make them because there is no market for them. How many enlarger manufacturers are still in business since the days of powerful, multi color LED available? De Vere is still making enlargers but their effort seems to make enlarger for digital files.
I think narrow wavelength is a good thing. The calibration would be different but we can do that with lots of testing. LED is a lot more efficient and thus less problem with heat. No big manufacturer will do it as we the darkroom users are few.

 

[AgX]

How many enlarger manufacturers are still in business since the days of powerful, multi color LED available? De Vere is still making enlargers but their effort seems to make enlarger for digital files.

In Germany alone there are still three manufacturers of enlargers:

Kaiser, Dunco, Kienzle

 

[DREW WILEY]

Tungsten halogen bulbs have a continuous spectrum which you can accurately filter with dichroic filters at any point along the spectrum. LED's are not. The concept of high-CRI, besides being largely a marketing term at this stage of the game, involves the blending of multiple bulbs to fool the eye into thinking you have a continuous spectrum. You don't. And you won't fool the film or paper. Every successful additive printer design ever made involved very tight dead-on tolerances. No difference with lasers. I happen to print on the same papers as laser devices like Lightjet. Works superbly. Films and papers are designed for distinct sensitivity peaks. The shape of the various dye sensitivity curves is a very important subject in its own right, but the peak sensitivity positions are standardized to correct nm RGB. But I don't need to argue. I've done it. Now go build your working unit with LED's if you think it is so damn easy. If you know what you are doing, you will be
able to consistently produce results every bit as good as a Lightjet or Lambda or Chromira, and hypothetically better, since it doesn't have
to go thru a scanner first.

 

[BetterSense]

If you know what you are doing, you will be able to consistently produce results every bit as good as a Lightjet or Lambda or Chromira, and hypothetically better, since it doesn't have to go thru a scanner first.

The thing is, I'm not so sure it would be "better" than lightjet, or RGB, or even subtractive, because of the dyes thing. At least it would be analog though. It's quite a risk to try, with little payoff especially since I'm not even big on color photography (I don't think it's going to catch on). I will definitely be thinking about it after I get my current darkroom finished.

 

[DREW WILEY]

The difference with Lightjet is that you scan first, do all your necessary corrective tweaks in something like PS, then print. With an additive
enlarger, you do your contrast etc adjustments analog if necessary, generally by silver masking, then print directly. Different kinds of film have their own personalities. Portra 160 is not Ektar, for example, is not Velvia. But a correctly made colorhead should work for any of them. Obviously, direct positive papers like Cibachrome are no longer made, so directly enlarging a positive chrome is no longer a practical possibility. Understanding film dyes takes some experience, but in every case, your centerpoint for each respective exposing light must be the same. How much wiggle room from narrow band you need is a much more complicated subject, and you need to understand how dichroic filter behave relative to angle of incidence and operating temperature. The big problem at the moment is that if you invest a lot of effort into an LED system, it might be impossible to maintain, since bulb designs are going to rapidly change. It might be worthwhile to prototype some
electronics, but like I said, it's rather premature to think you'll find anything close to ideal bulbs yet for this kind of project. There are a number of people taking the project halfway, and designing two-color VC printing heads with LED's, which is a much simpler problem.

 

[RPC]

Bumb...

(Actually there were two different enlargers. The older, substractive model accepts a special additive head.)

The Phillips enlarger can handle 6x6 cm. There are two additive color heads, one condenser-based and one diffusion-based. I own the condenser-based and it has plenty of light output for 11x14 prints. It runs cool. I find it works well and is easy to use and is not a "toy" as was earlier suggested. I got it off ebay 10 years ago for $75. A color head was also made for the Omega D 4x5 condenser enlargers, which I also have, and has the same lamphouse innards as the Phillips.

I did tri-color printing using Wratten filters #29, 99 and 98 (red, green, blue) under the lens which worked well until I found the Phillips.

 

[RPC]

Oops, should be Philips, not Phillips.

 

[DREW WILEY]

Sorry to offend you with the "toy" remark. As long as it's sufficient for your needs. I personally needed something additive that would punch
heavily masked 8x10 chromes onto 30X40 Cibachrome material. In other words, something literally about a thousand times brighter at working
apertures. That kind of situation demands some very different engineering.

 

[marfa.tx]

There is no sense writing rules for a game you will never play.

 

[BetterSense]

That may be the case but I do it all the time anyway.