How to test spectral sensitivity of a color negative stock?

[Seth Baldwin]

I'm trying to test the spectral sensitivity of an expired Kodak motion picture stock. How would i achieve this? Would i expose the film to isolated wavelengths at a single exposure value to see how each dye in the film responds after development?

[Sergey Surin]

We have such kind of service  Here in Moscow (laboratory of Mosfilm company) , I used it two weeks ago, they took 10 meters from each roll (in completely dark conditions) i gave them and then they made full check wth all information about how it holds in terms of sensitivity/dynamic range / fog level (hope I translate it right) 

And it seems that it could be done in every film developing laboratory all around the world so you just need to ask about it

[Giray Izcan]

It is called snip test.

[Seth Baldwin]

I've already done a clip test to establish dynamic range. But I want to find a way to test the individual sensitivity of each dye to particular wavelengths of light.

[David Mullen ASC]

Wouldn’t you also need a light meter that was accurate for specific wavelengths?

[Phil Rhodes]

For this you'd need a monochromator, which fires a beam of light through a diffraction grating to split it up into the spectrum, then passes the resulting light through a slot to select just one colour. The slot may be variable width. Given a sufficiently broadband light source (incandescent bulbs are widely used) light of any wavelength and bandwidth can be created. Monochromators are usually metered using a photomultiplier-based detector.

Quite whether it would be reasonable to apply all of this to testing suspect film stock is another matter.

[Seth Baldwin]

3 hours ago, David Mullen ASC said:

Wouldn’t you also need a light meter that was accurate for specific wavelengths?

Yeah, I'd likely need a spectrometer from Sekonic, can rent one thats fine. Or what phil said sounds promising. 

Edited May 21, 2021 by Seth Baldwin

[Sergey Surin]

If you meant individual  sensivity of each part of the spectrum (Red/green/blue) a have them too