Re: [Leica] RMS Granularity

["Paul T. Collura" <pcollura@epix.net>]

Irwin,

Glad to read from your post on granularity that you are apparently well and back in full form.  I hope you found American medical treatment to be satisfactory and caring.  Sorely missed you at the LHSA in Chicago.

Best Wishes,

Paul

> -----------------------------
>
> Date: Sat, 30 Oct 1999 21:13:18 +0200
> From: Erwin Puts <imxputs@knoware.nl>
> 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.
>
> Erwin
>