Effect of Infrared Light in Printing?

[everyXnewXday]

Does anyone know what effect infrared light has in the color printing process? I understand that papers are sensitive up to about 750nm (with the cyan forming layer peaking in sensitivity at about 700nm) but I'm wondering to what extent that infrared sensitivity is necessary to proper color? Or, in other words, would you get good (or better?) color using an IR cut filter (day at 680 or 700nm) on the enlarging lens, or is that infrared light essential to the response of the cyan layer?


I know that kodak specifies using "heat absorbing glass" when enlarging, but, as I understand it, this primarily blocks the higher frequency infrared "heat" wavelengths, and does much less for the 700-800nm range.


I know it's a weird question, but I'd appreciate any thoughts! Thanks!

 

[AgX]

In the neg-pos process the spectral sensitivity at the second stage is matched to the absorbtion characteristic of the image forming dyes of the primary stage.
This by no means needs to be related to the visible spectrum, or to a complimentary image to the scene, it even could be a deliberate false-colour match.

 

[everyXnewXday]

In the neg-pos process the spectral sensitivity at the second stage is matched to the absorbtion characteristic of the image forming dyes of the primary stage.
This by no means needs to be related to the visible spectrum, or to a complimentary image to the scene, it even could be a deliberate false-colour match.

Ok, yeah that makes sense. So, that being the case, it would seem that the paper expects a certain amount of IR light from the negative+light source and needs that for correct color balance. Thanks!

 

[JoJo]

Sensitivity of the paper rapidly drops at wavelength >700nm. You have 10times less sensitivity at 725 and 100times less sensitivity at 750nm.
So it is not really IR-sensitive. You can use IR-light at 800nm or above without any problems.
700nm is the area between visible and infrared light. Some protographers call 720nm "infrared", but this is still very close to visible light.

Joachim

 

[AgX]

Yes, one should differenciate between intentional spectral sensitivity and such due to "circumstances". For instance there had been colour camera-films that had actual sensitivity in the IR region, resulting in colour reoproduction on some subjects deviating from human perception. Finally that IR sensitivity was cut-off in emulsion design