How to interpret the difference between log sensitivity and relative log sensitivity in a spectral sensitivity curve?

[srb383]

Hi,

I'm trying to interpret the differences between log sensitivity and "relative" log sensitivity for a given color negative spectral sensitivity curve.

First off, how is spectral sensitivity for a given color negative measured and plotted?

Why is it the case for Kodak 2242, that it is plotted as "relative log sensitivity" with a status m optical density of 1.0>D-min. From (-3.0 to 1)

But for the original color negative (Vision3), it is plotted as "log sensitivity" with a status m optical density of 0.2>D-min. (From 0 to 4).

I'm confused how Status M densitometry relates to spectral sensitivity measurements plotted here. Because the y-axis for these graphs surely isn't status m optical densities right? What are they?

I have noticed that the wavelengths at which these dyes are apparently peak sensitive to, also happen to some what line up with the spectral response peaks of status m densitometry.

Peaks around 460nm for the yellow forming layer, 550nm for the magenta forming layer, and 650nm for the cyan forming layer seem to be observable as spikes in the spectral sensitivity curves of original color negative.

But the 650nm status m spectral response peak is not present for the cyan forming layer of Kodak 2242?

 

[Bill Burk]

The Y-Axis is the exposure that makes the mentioned density.

Where it’s not relative, the zero is “one meter candle second”, where it’s relative they are sparing you the detail because they think the graph is less confusing with non-negative numbers.

Status M is the right set of filters to use in the densitometer to make good readings from color negatives, while Status A would be for slides (that don’t have that orange mask to consider).

 

[laser]

Bill Burke: Good explanation.


I'll add a little.

The curves are created by using a light source or sources that are calibrated for intensity at typically one nm increments (350-1,000 nm) . The amount of light energy that is necessary to create a noted density is then plotted. The result is the curves.

Interpreting the curves by just looking at them tells what wavelengths will be recorded. Note that 1% sensitive doesn't create much of an image. Looking at the dyes created has little value except by comparing curves, you can tell if the dye sets are different. Just looking at the CMY dye curves doesn't offer much insight. The usefulness of the curves is apparent when calculating a cascaded print-through. This considers all or some portion of the elements in the scene, the film (data from the curves) , the printing system including similar data from the print material, and the observation conditions of the final reproduction etc. This in turn can be compared to the original scene. Such print-through studies are commonly done by manufacturers of photographic products. I doubt if many people would want to spend time doing this work. Optimizing the dye set takes a lot of computing power.


I will mention that the major influencers of the curves is the AgX grains with their dopants and spectral dyes and the created color coupler dyes that form the image.

Making KODAK Film is back in-print.

www.makingKODAKfilm.com

Bob

 

[Bill Burk]

Bill Burke: Good explanation.


I'll add a little.

The curves are created by using a light source or sources that are calibrated for intensity at typically one nm increments (350-1,000 nm) . The amount of light energy that is necessary to create a noted density is then plotted.

Bob

Thanks Bob Shanebrook,

This is the part that boggles my mind. That Kodak can figure the light energy at each nanometer.

I can’t even figure how many footlamberts I have left after converting my 100 FL standard tungsten source to daylight with an 80B filter.