Absorption spectra of color film dyes

alanrockwood · Apr 7, 2015

Does anyone know where to find absorption spectra for the dyes used in processed films of various technologies (E6, C41, ECN-2, K14 etc.)? I am not talking about the dyes used to sensitize the film layers, or the effective spectral sensitivities of the various layers, but rather the absorption spectra of the dyes used in the final image.

Thanks.

AgX · Apr 7, 2015

Those absorbtion spectra for specific films are typically not published.

You will find general spectra in the textbooks discussing the need for masking.

I rather would divide between chromogenic, chromolytic etc. dyes.

Xmas · Apr 7, 2015

AgX said:
Those absorbtion spectra for specific films are typically not published.

You will find general spectra in the textbooks discussing the need for masking.

I rather would divide between chromogenic, chromolytic etc. dyes.

You can still get an unmasked negative film - I think?

But the spectra of the masked absorption dye is further convoluted with the filtered emulsion layers sensitization dye, and the brain then'maps' this into a normal continuous spectra 'shadows at back of cave' some people cannot easily tolerate the result.

but e.g. Kodachrome was planned as a two colour layer before they relented and went to three.

AgX · Apr 7, 2015

You can still get an unmasked negative film - I think?

Agfa stated that the deficiencies of the image dyes have been compensated by other other means.

But the spectra of the masked absorption dye is further convoluted with the filtered emulsion layers sensitization dye, and the brain then'maps' this into a normal continuous spectra 'shadows at back of cave' some people cannot easily tolerate the result.

??

DREW WILEY · Apr 8, 2015

It's the hit between the idiosyncrasies in the specific film dyes in relation to the equivalent factor in a specific paper that counts. Far easier learned from practical print testing than industrial espionage or spending decades snooping film patents, and finally figuring it all out only
two decades after that particular film was withdrawn from the market. General theory is one thing, what goes into specific products and
why, something else. But I suspect that dye chemists apprentice in Voodoo first.

alanrockwood · Jan 21, 2018

Taking up this question again, in particular in the red or near infrared region... What are the typical cutoff wavelengths where the developed emulsion becomes nearly transparent? (I realize it will not be a sharp cutoff, but any information would be useful.) In other words, as we move from the green part of the spectrum to the red to extreme red to the infrared there will be a region of the absorption spectrum where the absorption is small and the film is nearly transparent. What would be a rough estimation for the wavelength range where the of the dye(s) in the developed emulsion absorb only very weakly.

Interimage · Jan 23, 2018

This information is available for ECN-2 process films. Here are the absorption spectra for Kodak 5219:

Rudeofus · Jan 23, 2018

I have no manufacturer supplied spectral density curves for you, but if an IR filter is what you are after, this page may be useful.

alanrockwood · Jan 24, 2018

Interimage said:
This information is available for ECN-2 process films. Here are the absorption spectra for Kodak 5219:

Thanks. I think this is the type of information I was after, but can you clarify something just to be sure? Is this the spectrum (in absorption form) of the developed film? I want to be sure it is not the data for the spectral sensitivity of the undeveloped film layers.

alanrockwood · Jan 24, 2018

Rudeofus said:
I have no manufacturer supplied spectral density curves for you, but if an IR filter is what you are after, this page may be useful.

Very interesting. Thanks.

AgX · Jan 24, 2018

alanrockwood said:
Is this the spectrum (in absorption form) of the developed film?

Yes.

For a specific chromogenic film. But see me remark above too (post #2).

Interimage · Jan 24, 2018

alanrockwood said:
Thanks. I think this is the type of information I was after, but can you clarify something just to be sure? Is this the spectrum (in absorption form) of the developed film? I want to be sure it is not the data for the spectral sensitivity of the undeveloped film layers.

As AgX stated, yes but for a specific film (in this case kodak 5219). Kodak describes the figure I posted above as follows:
"These curves depict the spectral absorptions of the dyes formed when the film is processed. They are useful for adjusting or optimizing any device that scans or prints the film."
The full spec sheet for 5219 can be found here

Rudeofus · Jan 25, 2018

It's quite interesting to see, how ECN-2 still has considerable density at 800nm wavelength, where slide film is already completely transparent. Therefore one can not blindly assume, that different emulsions have the same spectral density distribution.

Absorption spectra of color film dyes

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