Printing using RGB filters and multiple exposure rather than CMY?

grainyvision · Sep 22, 2018

So I read an article somewhere basically saying that the easy way to do color printing is with RGB filters, since only 1 filter is required and you simply vary the time for each exposure. I thought doing multiple exposures might be a hassle, but after getting the CMY filters and realizing I might need to stack 6 or more filters and keep them all clean (under the lens) and also organizing them by number, I'm realizing that maybe multiple exposures doesn't sound so bad. The recommendation I saw is for Wratten filters: #25 red, #99 green, #98 blue. I also saw a recommendation somewhere to use a darker red, like #70. Does anyone have any advice for this method or starting points for Fuji CA paper? What kind of ratio of times should I start with? Also, I bought some unopened old stock filters from eBay (still waiting on arrival), but other than that is there anywhere reasonable to get these filters brand new today? I've only seen them listed on B&H for $100 per filter for a 3x3" size (and 2-4 weeks "special order" delivery) which seems absolutely ridiculous

Young He · Sep 22, 2018

Could you link the article? Seems interesting.

I sometimes stick with the same filter pack for every box of paper, as they are similar, so I feel that even though it takes a few strips to adjust color balance, it’s easier than changing filters and times in total darkness.

I’m pretty sure eBay is the only cheap source for old wratten filters. You can get cheap rgb filters from amazon, but the quality is lacking, enough so that one doesn’t need fancy equipment to tell that they’re bad.

grainyvision · Sep 22, 2018

Young He said:
Could you link the article? Seems interesting.

I sometimes stick with the same filter pack for every box of paper, as they are similar, so I feel that even though it takes a few strips to adjust color balance, it’s easier than changing filters and times in total darkness.

I’m pretty sure eBay is the only cheap source for old wratten filters. You can get cheap rgb filters from amazon, but the quality is lacking, enough so that one doesn’t need fancy equipment to tell that they’re bad.

heh I actually have some cheap filters like that. I bought them for a different purpose, but I think they could be used for testing until the real filters come in. They were only like $20 for 12x12" sheets in 20 colors. The red sheet I've used before to cover my phone or laptop while B/W printing so that I can watch TV while printing and it works surprisingly well with no fogging issues, despite being fairly bright. The filters are also quite clear, but I'm sure they're not of deep enough color to be greatly effective for printing. Red and blue are fairly deep, but the green is pretty weak I think

Bill Burk · Sep 22, 2018

Sorry no specifics. But yes you can expose color print paper to three varying RGB exposures and have identical results as building a pack of CMY filters for a single exposure.

Good luck. I am sure you will find information how to do it, even if there isn’t specific advice for your paper.

MattKing · Sep 22, 2018

The challenges with using additive rather than subtractive filters are:
1) registration - you need to guard against movement/vibration, because otherwise three exposures will lead to fringing; and
2) the quality of the filters seems to matter more for additive work.
The Vivitar series of colour enlargers used an additive head (IIRC).

RPC · Sep 23, 2018

I have tried this before with excellent results. As Matt says eliminating vibration is necessary for sharp images. I anchored the enlarger head and body to the wall and changed filters between exposures by laying them on a filter holder (a little tricky in the dark). I used Wratten #29, 99, and 98 filters and varied exposure times. These are very narrow band filters, a requirement for precise color adjustments. IIRC the blue exposure was the longest and the red the shortest but YMMV. I don't remember exact times but they were under 10 seconds each for an 8x10 print with the Omega condenser head I used.

Later I acquired a Philips PCS150 which is an additive or tri-color enlarger which uses three lamps, each with a different filter and can make all three exposures simultaneously.

Martin Rickards · Sep 23, 2018

MattKing said:
The challenges with using additive rather than subtractive filters are:
1) registration - you need to guard against movement/vibration, because otherwise three exposures will lead to fringing; and
2) the quality of the filters seems to matter more for additive work.
The Vivitar series of colour enlargers used an additive head (IIRC).

I seem to remember that the Philips/Paterson enlargers also used additive printing.

thuggins · Oct 1, 2018

Please forgive my ignorance, as I do not do color printing. I also don't mean to hijack the thread.

But recently I have been studying the use of color separation using three B&W negatives made with RGB filters. It seems that one method for producing a print is similar to what is described here, but changing both the negative and its respective color filter. I am interested if anyone has done this and has any comments or insights to the process.

abruzzi · Oct 2, 2018

I would expect that with normal enlarging equipment, it would be near impossible to get a sharp image, since your replacing one negative with the next, and can only guess at alignment.

mshchem · Oct 2, 2018

abruzzi said:
I would expect that with normal enlarging equipment, it would be near impossible to get a sharp image, since your replacing one negative with the next, and can only guess at alignment.

Agreed. If you want to do additive buy an old Philips enlarger. Subtractive get a cheap used enlarger with a color head, or one with a filter drawer for acetate filters .

glbeas · Oct 2, 2018

thuggins said:
Please forgive my ignorance, as I do not do color printing. I also don't mean to hijack the thread.

But recently I have been studying the use of color separation using three B&W negatives made with RGB filters. It seems that one method for producing a print is similar to what is described here, but changing both the negative and its respective color filter. I am interested if anyone has done this and has any comments or insights to the process.

This is generally done contact printing on to the color paper using a register pin system. If the enlarger system has carriers that lock in to position you might get away with it if you can find a way to pin register your negatives.

jim10219 · Oct 2, 2018

thuggins said:
Please forgive my ignorance, as I do not do color printing. I also don't mean to hijack the thread.

But recently I have been studying the use of color separation using three B&W negatives made with RGB filters. It seems that one method for producing a print is similar to what is described here, but changing both the negative and its respective color filter. I am interested if anyone has done this and has any comments or insights to the process.

Yeah, I do this all of the time. It used to be the way they exposed plates in the printing industry before everything went digital and direct to plate in the 1990's. It's quite easy to do, really.

Basically you just set up your camera on a tripod, take one exposure with each filter, and make sure to compensate your exposure for the various filter factors. sometimes I'll just hold the filter over the lens rather than try to screw it on, that way I don't disturb the camera too much between shots, which will make registration by hand much easier later on. I also like to take a normal shot without a filter. It's usually a good idea to overexpose that shot by a few stops, but there are other ways to deal with that. I'll get to why in a second.

Then when you print, the red negative becomes the cyan positive, the green negative becomes the magenta positive, and the blue negative becomes the yellow positive. The unfiltered negative becomes the black positive, if you want to use it. You don't have to, but I find it generally gives a better looking print. The trick is, you want to back off the black to around 20% of it's traditional value. This is why I recommend over exposing it. Or you can under develop it. Or a combination of the two. Or you can back it off in a computer to around 20% or use less exposure time in the print stage. You have to figure out your own process for this.

The hard part will be getting everything in registration, especially if you're using an enlarger. That's why I only use this technique for contact prints or digital prints. Photoshop can auto align the colors for you (and just use the multiply layering option), or if contact printing, it helps to create some registration marks in the borders. If you're going to use an enlarger and RA4 paper for this, you'll probably need to design some kind of serious registration system since you'll be changing in and out negatives.

Mainecoonmaniac · Oct 2, 2018

I haven't printed color in years, but I was taught using yellow and magenta filters only. My brain is locked on that system and I'll find it impossible. But years ago, Minolta and Beseler made an RGB color head.
https://www.thephotoforum.com/threa...s-l-beseler-45a-colorline-7000-aristo.428933/

I think a lot of commercial color printers use the RGB system controlled by computers.

removed account4 · Oct 2, 2018

thuggins said:
Please forgive my ignorance, as I do not do color printing. I also don't mean to hijack the thread.

But recently I have been studying the use of color separation using three B&W negatives made with RGB filters. It seems that one method for producing a print is similar to what is described here, but changing both the negative and its respective color filter. I am interested if anyone has done this and has any comments or insights to the process.

this is also how "trichromes" are made
RGB usually separate exposures on pan film then printed on color paper.
there was a post here within the past month
about an artist who did these exposures all on the same sheet of film !
i wish i could remember her name... i've thought of making exposures all on the same sheet of film
but haven't had a chance to see if it would work out or not ..
i've separated black and white images and added color the same way, its kind of fun

OP good luck !
john

OzJohn · Oct 2, 2018

Apart from doing it once to prove to yourself that it works, I can't see why anyone would want to do additive colour printing using three filters. Before subtractive colour heads became available and/or affordable, additive offered a cheap way to try colour printing but used with an ordinary enlarger it is a complete PITA on several fronts. Others have mentioned registration issues. Add to this the timing challenges and the big one - it is impossible to dodge or burn during an additive exposure. The technique does lend itself to computer control and is the basis of automated printers. Certain enlargers, including those mentioned earlier and the Durst AC models were additive. The computer control in the ACs was similar in many ways to that found in analog minilabs of the era.

RPC · Oct 2, 2018

OzJohn said:
Apart from doing it once to prove to yourself that it works, I can't see why anyone would want to do additive colour printing using three filters. Before subtractive colour heads became available and/or affordable, additive offered a cheap way to try colour printing but used with an ordinary enlarger it is a complete PITA on several fronts. Others have mentioned registration issues. Add to this the timing challenges and the big one - it is impossible to dodge or burn during an additive exposure. The technique does lend itself to computer control and is the basis of automated printers. Certain enlargers, including those mentioned earlier and the Durst AC models were additive. The computer control in the ACs was similar in many ways to that found in analog minilabs of the era.

The OP stated he otherwise would have to stack CMY filters under the lens. This could cause significant image degradation. (Apparently his enlarger has no filter drawer.) So RGB filters would be a better way. This was the reason I did it years ago until I purchased a colorhead enlarger. For ordinary printing there is really no other reason to do it. Years ago paper response was not as narrow band as today and RGB printing could sometimes give better quality than subtractive printing but today's papers are much more narrow band and so there really is no difference between the two qualitywise.

glbeas · Oct 2, 2018

In a case where the enlarger has no filter drawer its easy enough to just stack the filters on top of the negative carrier in most models.

RPC · Oct 3, 2018

There have been times when I have used CMY filters but in IMHO changing them out and making precise changes in filtration is as much of a hassle, if not more, than doing it with RGB filters.

With a little ingenuity one can figure out quick and easy ways to place the RGB filters under the lens and switch them around, e.g., some sort of a turret system.

foc · Oct 3, 2018

When I started commercial photo printing back in the late 1970's, I was trained on one of these

It was basically an enlarger enclosed in a lighttight box with roll paper transported over an easel. You put the neg into the carrier (over a little inbuilt lightbox) and pushed the carrier into the light source path. Exposure was by the colour additive method (RGB) and the control panel was in CMY. The exposure timed by a single photo electric cell, that gave each colour exposure it's own time. If you touched the carrier and banged against the unit during the exposure you got colour misregistration. The filters were on a motorised wheel between the light source and neg.

This is the only time I saw additive colour printing, any enlarger I saw either has filter drawer or colour dichrocic head.

As had been mentioned above, I am sure you could make a DIY job that would suit your enlarger but image/enlarger shake could be a big problem

EdSawyer · Oct 3, 2018

Additive color printing will generally always be better to a degree, than CMY subtractive color, for RA4. Less color crossover, among other things.

The Minolta/Beseler 45A color head uses pulsed flash tubes and RGB filters for additive printing. I think it's the best color head available in that size, and a bargain on the used market. Also has a great analyzer and meter built-in.

Chan Tran · Oct 3, 2018

When I worked with the Noritsu QSS-2300 I found that it has a light source with dichroic filters and we use it to set for what we called "Dead Heat" that is correct filtration for the standard negative. During printing the machine measures the negative (kind of color analyzer) and correct for exposure and color balance via 3 different RGB filters that move in and out of the light path via solenoid.
I thought of doing so with my own enlarger but I am afraid that when the filters move it may set up vibration.

darkroommike · Oct 3, 2018

I've done additive printing on the old Nord machine, others have mentioned the Phillips and the Beseler 45A. My recollection of the Nord was that it was really, really slow. Unicolor also made an additive printing filter kit at one time with three filters and an integrator on a color wheel, I suspect that it too was really, really slow.

grainyvision · Oct 3, 2018

glbeas said:
In a case where the enlarger has no filter drawer its easy enough to just stack the filters on top of the negative carrier in most models.

I think this is possible on mine, but that would definitely scratch the filters and potentially cause too much light leaking when I have to deal with 5+ filters. Also, my negative holders don't hold the negative nearly as tight as I'd like, so I'd probably have to reposition everything with each filter adjustment. My enlarger is one of those two color ones for B/W printing with a blend of blue and green light. I guess because it has built in filtration, Beseller in their infinite knowledge didn't think that a filter drawer was necessary... oh and the negative holders have a spring "feature" that quickly breaks, had to take a torch to one to remove the spring to make the holder usable again. Oh, and this enlarger originally had a "computer designed exposure control" feature so that you could use the same time for every contrast grade with the same exposure.. only problem was that it effectively blocked 90% of light until you got above grade 4. My "normal" exposure times were around 45s at f/8. I took that apart and removed the exposure control feature and ended up just using some ilford multigrade filters in the holder thing for red glass, and using only white light. With ilford filters it's easier to gauge exposure with contrast adjustments, and after I removed the exposure control the contrast grades got really wonky. I'm sure with enough analysis I could figure out where true grade 2.5 is and such, but the markings on the enlarger itself for 2.5 is really around grade 1.... Anyway, enough ranting about how much I hate the 67VC enlarger, anyone interested in buying/trading one from me? Preferably for a color head?

thuggins · Oct 4, 2018

OzJohn said:
Apart from doing it once to prove to yourself that it works, I can't see why anyone would want to do additive colour printing using three filters.

Thanks for all the replies.

The problem with registration would be very tough with an enlarger, and this process would obviously be much more practical with contact prints. My initial interest came from pondering what options we might have if chromogenic films ceased to be available. But in researching it became apparent that it is a different artform in it's own right. As the image(s) retain the silver rather than being formed by dye clouds, the contrast and overall "look" of the image would have to be different. This may be lost to some extent when printing negatives on a chromogenic paper, but a projected positive must look notably different from a "normal" transparency.

Prof_Pixel · Oct 4, 2018

If I remember correctly, there was a company that made a nice additive printing kit in the early ‘60s. It had a strip that contained a red, green and blue filter; a holder for the strip that mounted under the lens; a blurring filter to ‘integrate the image’; and a ‘step’ filter to put over your paper when making a test print. To make a test print, you put your color negative in your enlarger and adjusted size and focus. You then put the ‘step’ filter over your color paper in your easel and put the ‘blurring’ filter in the holder beneath the enlarger lens. You then put the color filter strip in the holder and made a standard exposure time thru each filter (it was notched to make positioning it easy). After processing, you looked at the print to determine the best exposure time for each filter. It worked OK as an experiment.

Printing using RGB filters and multiple exposure rather than CMY?

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