Additive color printing brainstorming

[Mr Bill]

Response to post 24 - use of a subtractive dichroic filter system

Bill;

I was referring to it. And, the method you suggest was usable but not very successful due to the broad cut of the filter compared to the blue light. The filter did not cut off all of the blue light. That is my point. The subtractive filters are broader in bandwidth than the additiive filters and thus "leak". You need a special, high density yellow, magenta and cyan filter set to get it to work so that when superposed, all 3 = BLACK and not gray! Test it yourself and you will see.

PE

Sorry I've been away a bit. Yes, this "special high density yellow, magenta, and cyan filter set..." is exactly what I'm talking about. Here's what I said about them in post #5, "Somewhere in the light path are what they call "filter paddles", equipped with sharp-cutting cyan, magenta, and yellow dichroic filters."

Perhaps I should have attached filter response curves, A brief word from "Applied Photographic Opics", by S Ray (1002), section 10.6.1, on dielectric/dichroic filters."...such filters...are used in colour printing applications. The near-rectangular spectral transmittance profile is superior to other forms of printing filters. In addition, they do not fade and can be used in intense, collimated light."

And, the method you suggest was usable but not very successful due to the broad cut of the filter compared to the blue light.

In truth, the method I've described, use of dichroic filter paddles, with subtractive (CMY) makeup, was an industry workhorse method for many years. If you used a lab equipped with Kodak PVAC (analyzers), or its predecessor, the VCNA, they were likely using Nord or Lucht package printers equipped with such lamphouses. When using printers that cost nearly as much as a small house, the ability to print twice as fast could mean that you don't need to buy another printer. I think, perhaps, that Kodak may have not built any such lamphouses, but it would not have been unusual to hear of Kodak S-printers equipped with Lucht lamphouses. I would imagine that this has been discussed in older issues of Kodak Tech Tips, a publication generally only available to finishing labs.

In the early to mid 1980s, with the advent of 1-hour mini-labs, the majority also adopted this method. However, with the advent of digital printing, these conventional optical systems gradually became mostly obsolete.

I post this, as, like you, I am also worried about people misunderstanding. Unfortunately, there seems to be little public information available on these, so I can't offer any supporting data.

Also, unfortunately, this methodology probably won't work for the original poster, who already has a lamphouse system. If anyone else contemplates one of these dichroic filter paddle systems, you should know that 1) the filters should ideally be in a nearly collimated beam, and 2) they are generally small in diameter, and likely wouldn't cover your negative. So you would build them into the light path at an early stage, and possibly go into an integrating chamber.

 

[Photo Engineer]

Well, Bill, you have enumerated most of the problems but left out cost! These dicrhoic sharp subtractive filters are quite expensive and have to be in the range far above our normal 0 - 100 y/m/c sets to be effective. As I said, yes they were used, but due to the cost and the calibration as well as the difficulty in adjusting filtration, they died out gradually.

The first Kodak enlarger was an additive system designed by Sir Robert Hunt of Kodak Harrow. We just turned an early version over to George Eastman House.

And yes, I do have a rather complete set of Tech Tips, but have never run across this system due to its complexity and rarity. I may have to review my collection though to make sure that is correct. I may have forgotten over the years.

Thanks.

PE

 

[nyoung]

Why not seek out a Phillips PCS 150 color head/controller. Does everything you say you want to do.

 

[Mr Bill]

Hi PE. Yes, expensive new. In my first post, I alluded to the possibility of finding these on the surplus market. I should have been more clear about it. Since there were plenty of original spare parts, but the machines using them went obsolete, these things should have almost no market value. In fact, a great many printers were simply scrapped.

It's possible that used equipment dealers may have junk piles including the entire light source assemblies. The average person wouldn't be able to use these, but the OP is knowledgeable about electronics. Basically, one needs, at minimum, the circuitry to drive and hold three rotary solenoids (typical about 1/4 turn, on/off). Although I couldn't personally do this, it seems to me easier than trying to drive a rotary filter turret to the correct position for three separate exposures, shuttering the light source in between, etc.

Also, BTW, this thread started with, "This is a conceptual exercise..."

 

[Photo Engineer]

Bill;

I have dug out and searched my "Kodak Professional Notes", sent to professional photographers and photofinishers between 1955 and about 1965 to teach many of the technical items of B&W and color photography. Interestingly enough although I remember what you describe, and probably saw it in action, it is not mentioned in any of these notes. They simply describe R/G/B and C/M/Y printing methods in detail.

I do remember that the sensor integrated to a neutral for the average negative, and that the timers were set to give an integrated neutral by varying the timing on the solenoids. (does this sound right?) In any event, tuning and keeping the solenoid timing was difficult and ended up being more difficult than just dialing in the M+Y filtration that gave the sensor its neutral point.

In fact, that is the method that is used now with most color analyzers just getting one good print and then setting the 3 sensors to zero. Then any new negative just needs to have the zero for it set with Y+M and aperture. Done in a big printer this can be very fast.

Thanks for that old information. You must be about as old as I am!

PE

 

[Mr Bill]

Nah... I think you have a couple handfuls of years on me - your Professional Notes are before my time. In 1965 I was just a punk kid, first becoming very serious about photography. I don't remember an exact time frame for the filter paddle systems, but it was some time after the DEC PDP 11(?) computer was out. Bremson Data Systems had built a complete photofinishing control system, including a printer controller. In their pro-lab system, negs would be analyzed on a VCNA/PVAC, and the data would be piped to an appropriate printer. With the Lucht lamphouse system, the Bremson controller could run the individual print color exposures for any negative, as well as operate the individual lens decks in a package printer. So in my experience, the print data had been predetermined, and was simply being acted at the printer.

A few years later, early 1980s, 6-hour and then 1-hour mini-labs began to proliferate. The most common units also used the CMY filter paddle method, but was based on tri-color sensors, integrating to gray, as you mentioned. Eventually, CCD scanners entered into the picture, so very sophisticated (for the time) scene analysis was now possible. Eventually, everything went to digital exposures, and the previous optical systems were mostly phased out.

I have to leave my computer, now, but it's been fun reminiscing!

 

[Photo Engineer]

Thanks Bill.

I remember the Model V printer for color and later the model 2000. At Kodak, we used the PDP8 and then the PDP12? Not sure about the latter. Many Kodak systems used the Intel 4004 chip set even though the 8008 and 8088 were out by then. Intel made them just for Kodak, special order IIRC. They may have been used in the early printers.

The Model V, IIRC, used R/G/B to get the best color, as the early color paper had poor separation between spectral sensitivities. They even considered putting a "separation" type filter into the paper to improve this and allow white light printing that gave separation type results, but then they got better sensitizing dyes for the paper.

Long story and history. Some things worked and some things did not. Some things worked but were either too complex, too expensive or both.

Enjoy your evening.

PE

 

[Ronald Moravec]

You will have a hard time burn & dodge if you make sequential exposures.

I have two enlargers with an RGB 3 bulb set up. Each is controlled by a separate resistor and all three by one timer.

There is a RB or G dichroic in front of each bulb.

I would offer the name, but I forget.

 

[Nicholas Lindan]

If the thing is computer controlled there is no reason you can't have CMY controls and an RGB light source. It's just a mathematical transform; Photoshop does the reverse on the fly when you open a CMY image and display it on an RGB monitor.

If there isn't enough confusion in your life then you can have a switch that switches the controls between CMY and RGB - you can try printing with both in the same session.

 

[BetterSense]

If the thing is computer controlled there is no reason you can't have CMY controls and an RGB light source.

RGB light source would be difficult and expensive to engineer. Using RGB filters would be cheap and work with my existing enlargers. The point about not being able to D&B is well taken.

 

[darkroommike]

Jumping into this really late, but it's only 7 above, there was a commercial enlarger/printer that used RGB, actually a pretty fancy setup, but yes, all the objections raised so far were true for this. I don't mean the Minolta Beseler 45a which was the last such system I am aware of or the Phillips units which were kind of DOA, but the Nord, anyone else remember the Nord? It was actually used for commercial printing once upon a time, the state college I used to work for for got one used, surplus in the 70's from the SD Highway Patrol, along with a roll easel and a Kreonite nitrogen burst color print processor.

 

[Mr Bill]

but the Nord, anyone else remember the Nord?

Hi, I used to keep my day job out of the discussions, but finally changed my mind. I spent a lot of years with a large chain outfit where we had something like 65 Nord package printers, over half in our main lab. Originally they used filter drawers, but when Lucht developed the lamphouses I mentioned we converted to those. Each printer could knock out a 600 ft roll of 10 inch paper, around 900 8x10 "units" in well under an hour.

It's not very common to run into someone who even knows what a Nord printer is. They were built by Photo Control, makers of Camerz cameras, etc.

 

[ic-racer]

Why not seek out a Phillips PCS 150 color head/controller. Does everything you say you want to do.

Interesting to see this old thread revived. In the intervening time, I actually have acquired one of these nice RGB additive enlargers.

 

[ic-racer]

In an additive system, adding opposite colors does not add ND, it removes ND; the image on the baseboard is brighter.

 

[Malcolm Stewart]

Sorry for the late response, but have only just found this thread.

Two of us used Wratten filters back in 1962 when using the additive method, printing graduation portraits for our fellow students.
We used non-masked Agfa CN17 or Agfa CN14 film, and printed on the newly available to amateurs Ilford Colour paper of the period. Sadly, although we did use the optional anti-fade final bath, our prints soon faded when placed on view in the proud parents' homes. Amazingly, none of our student friends asked for their money back. I do remember exposure times being of the order of 3 to 5 minutes. The enlarger was a basic 35mm Rowi, with its normal mains lamp.

 

[RPC]

I have tried additive, sometimes called tri-color printing, in the past with excellent results using #29, 99, and 98 Wratten filters.

In the past the spectral response of the color papers would have made this the superior way to get the most accurate print colors, but with today's papers I doubt it makes any difference. In tests I have run to compare it with subtractive, I could see no difference.

On the other hand, due to the narrow-band nature of the filters, getting to the precise desired color balance may be a bit easier and faster once you are experienced with it.

 

[John51]

RH Designs do a RGB light source. Maybe it could be modded for colour? Or a diy version?

Assuming that LEDs can be dimmed, the exposure time can be constant, say 10 seconds. The operator would only need to control red and blue. Add those values up and green is 100 minus whatever red and blue added up to. If the maths get a bit messy because different wavelengths = different reciprocity, then input the data from the initial tests to the Rasberry Pi and let it calculate it for each exposure.

 

[~andi]

The Heiland LED modules can be used for color processes (they advertise it for RA4 and Ilfochrome). You just need the right control unit. I think they have sizes up to 8x10 in stock but probably can build to any size required. How good this works... no clue. However, I would assume if Heiland offers it, it works very well (they're reputable company). Anyways, my point is, it can be done with LEDs successfully.

~andi

Links:
http://heilandelectronic.de/led_kaltlicht
http://heilandelectronic.de/color_timer

 

[Ronald Moravec]

burn & dodge are near impossible with 3 consecutive exposures. Color prints made with my tricolor 3 bulb /3 filter are beautiful

 

[Photo Engineer]

Yep, burning and dodging are nearly impossible. In fact, they are actually impossible.

PE

 

[nworth]

A related possibility is to use RGB LEDs as a light source. You can control the intensity of each color by controlling the current to the corresponding chip(s). The color from LEDs is decently pure, although the blue and pure green versions have a fairly wide bandwidth. With high power RGB LEDs now available, such a light source should be practical. Calibration may be an interesting exercise. As mentioned above, the CC values of subtractive filters correspond to the amount of light of the complementary color that they absorb. You should be able to put together a table relating RGB values (and the corresponding lamp currents) to CC values, which would make operation simpler.

 

[bvy]

I'm intrigued. I ordered a Beseler kit today with a tri color (RGB) filter that slides under the lens, and an additive color calculator that sits on the paper for making test prints. A diffuser swings under the lens for making the test print, and you read off the exposure times for each of the three filters. Easy as pie! Well, that's the theory. More than anything, I want to see how the prints compare. Also, I'm hoping it will speed up making prints that don't require any localized treatment (e.g. dodging and burning).

 

[Photo Engineer]

Although, 3 color printing can give some spectacular effects using a dodging burning technique. Kind of like colored halos.

PE

 

[DREW WILEY]

A registered mask can substitute for dodging and burning and do it predictably. The Devil is in the details of course. But not difficult once you've learned the ropes. But I have both 4x5 and 8x10 simultaneous-tricolor RGB colorheads, which make all of this very easy.

 

[thornhill]

Where can you buy these filters? I can't find them at Freestyle. I have a Lee/Roscoe gel swatchbook; do you think there is equivalent RGB filters in there I could use?

Edmund Scientific sells them, or used to.
I'll put another plug for the Philips Tri-one system. I used one before but needed more power and coverage when I went 4x5, so I bought a second one at auction and ganged the two of them together into a single home made color head with two controllers. It worked very well with considerable adjustability. I'd be using it now except it sits on a Beseler condenser head and I decided to go diffusion. This might be a fairly low tech way of achieving your goal.

Arrrrgh, I just noticed that I'd answered a question from eight years ago. Oh well.