[Bill Munns]

Just curious if anyone knows or can provide links to data on the actual measurable size (or average size) for the emulsion grain particles for Kodachrome 25, measured in microns or fractions of an inch?

Also, would the grain particle size be different, in average size, on the different color layers?

Thanks for any info on this request.

Bill

[Dominic Case]

Bill Munns, on Jan 27 2010, 09:14 AM, said:

Just curious if anyone knows or can provide links to data on the actual measurable size (or average size) for the emulsion grain particles for Kodachrome 25, measured in microns or fractions of an inch?

Also, would the grain particle size be different, in average size, on the different color layers?

Thanks for any info on this request.

Bill

The "actual grain size" is a hard thing to quantify in any film, possibly even harder in a reversal film. What you actually have in the processed image is dye clouds that are formed wherever silver grains were not exposed and formed in the first development. What the film starts with is a very broad range of grain/crystal sizes. The largest ones are exposed first, the smaller ones are only exposed by brighter light: so the average grain size is also dependent on exposure and density. For another thing, dye clouds tend to cluster together, so aren't the same thing as discreet grains at all.

And looking for the "average" isn't even as easy as looking for (e.g.) the average height of an adult human, which follows normal distribution (a bell curve) over a very limited range. What is the average size of a fish might be a better analogy.

BUt this link is one that discusses the metrics that are usually used to measure these things, such as rms granularity and resolution in lppmm:
http://cool.conserva...tal-projection/

By and large, K25 was pretty fine-grained for its time, but I think a medium speed negative film would give it a good run for its money today. (Given that its hard to compare neg with reversal for the reasons above).