Colour calibration, just wondering

Martin Rickards · Jan 22, 2018

I was looking at exposed colour negatives, or rather the cassette end unexposed negatives and wondered whether by superimposing this with a black and white negative and adjusting the print filtration to give the most neutral black and white test print on colour paper, whether this would be easier than trying to judge and correct colour casts..

BMbikerider · Jan 22, 2018

Yes you can do this but is may take a lot of fiddling about. I printed quite a few B&W negs onto RA4 paper and the closest I was able to get was a warm tone very similar to Ilford Fibre based warmtone B&W paper. If you can fit a piece if 120 colour negative above your negative carrier this will be better because you reduce the risk of trapping dust between the two films and because it will be bigger than a 35mm negative there is no risk of light leakage around the side of the small negative.

There is also a possible risk that unless you use the same film and develop exactly the same you can get a colour shift anyway. To be quite honest, whilst it is possible I think you are going to give yourself a lot of work.

Another way which will almost certainly eliminate the problems associated with different films/processing is to take a picture of a 37% grey card at the start of the cassette and print that one 1st. Use flash for this exposure which will ensure you are using a constant light source. Any variation with colour tones compared with a print of the grey card will be immediately obvious and easily corrected.

foc · Jan 22, 2018

I tried this in the mid 1980's with Ilford XP1 exposed with a plain orange mask (blank neg) above the carrier, using a commercial lab Durst printer and exposing onto EP2 paper (this was in a commercial lab). It was part of an experiment to see could we print B&W negs on colour paper and achieve true B&W prints.

The answer was yes and no. Yes we could get a true B&W print from a neg but it took a lot of colour filtration tests. Then when we used the same or simular filtration for a different neg we got different results. Basically we had to colour test each neg. Just bear in mind that this was commercial equipment and the printer was programmed to auto correct colour negs and because we got inconsistent results we abandoned it.

I am sure you could achieve better results with a colour head enlarger but IMO there are too many variables.

DREW WILEY · Jan 31, 2018

No. Panchromatic film has spectral bias, including depressed green sensitivity. You need to look at the spectrogram for the specific pan film in mind. If you attempt this, you need to set an enlarger colorhead to a standardized Kelvin color temp. With current Portra and Ektar films 5000K seems to work best with my equip making accurate interpositives. Then to this you need to process an unexposed sheet of the same kind of color neg film involved to get an orangish filter exactly matching the orange mask. Place this in the 5000K lightpath. Finally, to correct for deficient green, add a pale YG filter (Wratten 11 or Hoya XO). This works well with TMax100 film to get a neutral white light interpositives. But to do it with separate RGB exposures is way more complicated because you have to find the sweet spot in both exposure time and development to match all three curves. A lot of work. Good to learn if you need true color separations for assembly printing, but a thousand times more work to balance RA4 prints. ... like six months versus half an hour.

DREW WILEY · Jan 31, 2018

If you try this on b&w paper instead of film, even more complicated to get consistency. With RGB film separations exposed via pin registered, an RA4 print could be made with sequential exposures using a precision registered neg carrier. I'll do it one of these days. I have the gear. I've seen it done before. If you have a ballgame with 700 innings instead of 9, you might get to second base. I learned the ropes for the sake of dye transfer printing. No need for simple RA4.

Martin Rickards · Jan 31, 2018

DREW WILEY said:
No. Panchromatic film has spectral bias, including depressed green sensitivity. You need to look at the spectrogram for the specific pan film in mind. If you attempt this, you need to set an enlarger colorhead to a standardized Kelvin color temp. With current Portra and Ektar films 5000K seems to work best with my equip making accurate interpositives. Then to this you need to process an unexposed sheet of the same kind of color neg film involved to get an orangish filter exactly matching the orange mask. Place this in the 5000K lightpath. Finally, to correct for deficient green, add a pale YG filter (Wratten 11 or Hoya XO). This works well with TMax100 film to get a neutral white light interpositives. But to do it with separate RGB exposures is way more complicated because you have to find the sweet spot in both exposure time and development to match all three curves. A lot of work. Good to learn if you need true color separations for assembly printing, but a thousand times more work to balance RA4 prints. ... like six months versus half an hour.

My understanding is that a light source emitting at only 5000º K will not produce colour prints. A broad source comprising all wavelengths of the visible spectrum is necessary.

mnemosyne · Jan 31, 2018

Martin Rickards said:
My understanding is that a light source emitting at only 5000º K will not produce colour prints. A broad source comprising all wavelengths of the visible spectrum is necessary.

"5000K" is not a wavelength, it merely describes the general "temperature" of the light (which parts of the spectrum dominate), it tells you nothing about the "quality" of the light in the sense of completeness of the spectrum. It may refer to full spectrum light source like natural daylight or tungsten light or halogen light or it may refer to a non continuous spectrum ligth source like LED light, fluorescent light etc

Back to the topic, reading your initial post I am still not sure what you are trying to achieve. Facilitating color balancing when printing color negatives on RA4 paper or finding a "neutral gray" when printing b&w negatives on RA4 paper?

Martin Rickards · Jan 31, 2018

It was to ease calibrating filtration on RA4 paper, it seemingly being easier to judge a neutral B&W image than a colour image.

DREW WILEY · Jan 31, 2018

Do you have a colorhead? There are plenty of past threads on calibrating paper. It's easy. No need to cross a jungle barefoot.

DREW WILEY · Jan 31, 2018

Learning how to see specific hues is more a matter of experience and having a good reference target and master negative for comparison. I like the MacBeath Color Checker Chart.

Martin Rickards · Jan 31, 2018

Yes I have a colour head, but haven't printed in color for about 15 years. Getting enough experience to balance prints again is likely to be a long job

Mainecoonmaniac · Jan 31, 2018

Martin Rickards said:
I was looking at exposed colour negatives, or rather the cassette end unexposed negatives and wondered whether by superimposing this with a black and white negative and adjusting the print filtration to give the most neutral black and white test print on colour paper, whether this would be easier than trying to judge and correct colour casts..

You can also shoot a 50% gray card or a step wedge too.

Colour calibration, just wondering

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