Originally Posted by
Photo Engineer
To answer a few questions....
If you photograph a neutral density scale and enlarge it then read it, you will get some measure of granularity which can be loosely defined as the variation in density over a given area of space. It is the reverse of taking the small image and reading it with a microdensitometer. So, you do not need a microscope at all. All you need to do is magnify an image and measure density fluctuations in a straight line across the surface of a print. The root mean square of this fluctuation might be considered the grain at that density. Doing it repeatedly over all densities and then plotting the resultant RMS values will give you "RMS Granularity" of the film as a function of density or exposure.
As for motion picture films, Mike is partially correct. Color Motion Picture films are the finest grained of all color negative and print films. The fineness of grain and resolution are astounding. But, nothing is perfect. In fact, there is a minimum value for grain due to noise. You can cast a pure grainless dye on transparent support, and it will yield a finite value for RMSG due to the noise in the measuring system.
PE
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