>
> I'd have never guessed that. I could easily see how one could soften
> selectively, but didn't see how the grain detail could be retained at
> the same time. Any idea why/how that works?
>
Because a B&W negative is not continuous tone--it's actually closer to being
a half-tone, but with randomly placed, oriented and sized "dots".
In a split-grade print, you expose the two emulsion layers of the print
separately. The grain tends to appear more in the hard-grade layer than the
soft-grade layer. Grain that does appear in the soft-grade layer is usually
more disturbing to the human eye as it would appear in the sky, in gentle
highlights, etc. By diffusing (really, by only a portion of the exposure,
not the entire thing) the soft-grade exposure, you can smooth out the higher
tones and even blur the image, but "edge-detail" is maintained as
dark-to-light transitions are governed by the hard-grade exposure.
A trick I learned from my dad back in my childhood days--long before
split-grade was ever dreamed of, was extremely valuable for portraits.
Between 1/4 and 1/3 of the exposure was made through a wrinkly sheet of
cellophane plastic that we'd have in motion. The closer to the lens, the
more diffuse the Gaussian blur was. Typically, you'd use it about halfway
between the lens and the paper. By limiting it to 1/4 to 1/3 of the
exposure, the effect was pretty subtle, but you could really notice the
difference in smoothness of skin.
AG (In the dark since 1969) Schnozz
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