Quote Originally Posted by dnmilikan
Since I am beginning to use incident metering more then I once did, I have been thinking of using a densitometer to read filters as a more accurate means of determining the spectral response and filter factors.
Does this make sense? Has anyone done this?
It *does* make sense - but ...

"Spectral response" (energy transmission at a given frequency) is usually determined with the use of a "Spectrophotometer". This is a device consisting (simplified to beat @#$@#$) where there is a controlled w-i-d-e spectrum light source, a *very* sensitive device for reading light energy, a controllable "slit" and a and a rotatable (and controllable) prism. In use, the prism and slit are set to a given angle to allow a narrow beam of light at a given frequency, the energy output is measured without the medium in question; then with the medium. The two values are then compared and a transmission attenuation factor is calculated for that one specific wavelength.
The prism is then rotated to supply a different wavelength of light; before and after measurements are again taken ... etc.

After the required range has been investigated, the spectral transmission is then plotted.

At least that *was* the way it was done, back in the neolithic ("neo" indicates "new" - what indicates "old"?) age, before fancy computers and lazy optical technicians. Now, I imagine, one turns the wildly expensive machine ON, stuffs the "filter" into it and pushes a button.

You speak of "channels" with the densitometer. I would guess that there are a few at discrete wavelengths of light. Probably the values at those particular wavelengths would be valid; I can't see why they would not. .

However, all films - black and white as well as color, are sensitive to energy at a wide range of wavelengths - so I'm not sure how useful the (accurate) information would be.

Comment: Ho boy!! Memories of an Optical Bench .... and a sore back...