Archived posting to the Leica Users Group, 1999/10/30

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Subject: RE: [Leica] RMS granularity
From: Jem Kime <>
Date: Sat, 30 Oct 1999 20:47:32 +0100

No matter that I didn't have the staying power to decipher your in-depth 
post (and that's partly because I use slide film only once in a blue moon) 
it's great to have you back.
Hope you're feeling better and 100% real soon.

best regards,

- -----Original Message-----
From:	Erwin Puts []
Sent:	30 October 1999 20:13
Subject:	[Leica] RMS granularity

The new Provia 100F has a published RMS granularity value of 9 and
is, according to Fuji the lowest value of any 100 speed slide film. I
do not wish to dispute this claim. Film manufacturers are
conservative in their claims. But what does it mean? It is being
cited as a premium characteristic, that distinguishes this film.
First someRMS  figures.
Provia (old); 	10
Velvia		9
Astia 		10
Provia F (new)	9
Fujicolor 100	4
Fujicolor 400	5
Fujicolor 800	5

So we see that even an 800ISO color neg film is much finer grained
than a very fine grained slide film.
The RMS granularity is a figure derived as follows.
A microdensitometer with a circular aperture of 48 micron scans the
uniformly exposed area of an emulsion. Because of grain distribution
the density of the emulsion is not equal (as it should be because of
uniform exposure). The density thus fluctuates and these fluctuations
indicate the presence of grain. The variability of the fluctuations
around the mean is well represented by the deviation which is the RMS
value. Remark that it is a fluctuation around the mean and because of
the reading aperture of 48 micron IS ONLY VALID at a magnification of
12 times. At any other magnification (usual for slide film) the
correlation between graininess and RMS value may not hold.
The other point of this measure is worth noticing: the viewer of the
grain pattern looks at such a distance that the apparent grain
pattern seems to  be not visible or blends. We may wish to ask
whether this threshold value  is of overriding importance. If the
viewer still sees a slight grain pattern (disregarding here all kinds
of psychological and physiological factors), would he/she detect a
significantly larger grain? And if so what is more important: light
scatter because of finer grain which will reduce the impression of
sharpness quite a lot or the fine grain impression. Furthermore: the
chracteristics of B&~W grain and of dye couplers are very different.
Because of the uniformly spread dye couplers  the random fluctutaion
around the mean is reduced. So the value of 5 or 9 for dye coupler
films does not indicate the same grain impression a sa value of 11
(Kchrome 25) or a 13 for B&W negative film.
As so often: any single value taken out of context and without
reference to the measurement parameters may be quite misleading.