Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul Roark" 
<paul.roark@v...> wrote:
>
> > 
> > Paul...you're actually measuring this? How? With what tool?
> 
> I scan a featureless film -- like a clear blue sky shot.  (Actually 
I use a
> ground glass over the lens to make frames for comparing grain.  
Also, I
> shoot a step wedge type target with plain patches for calibrating my
> development of film.)  Then in Photoshop the Histogram gives 
information
> regarding the standard deviation within a selected area.  If the 
film and
> scan were perfect, this would be 0 -- all pixels would have the same
> density.  However, due to grain and other sources of density 
differences,
> not all pixels are the same value.  The more they deviate from each 
other,
> the higher the measure of "standard deviation."  Most of the density
> differences appears to be due to grain.
> 

Well, if the use of a diffuser results in any measureable reduction
in (the standard deviation of) the distribution of the pixel values
for a uniform target, would not this imply that the actual
spread is due to the aliasing introduced by the scanner rather than
the graininess of the negative ?  I  did a similar set of 
measurements with a Nikon LS4000 and Neopan Acros as well as NP-400
(using CoolScan 4.12) over a year ago but the variation from one 
scan to the next were large enough that I gave up on the idea of 
getting smooth tones from a film scanner.

It would be great, though, if you could post your (raw) readings 
(mean and standard deviations) for the film base+fog, fully exposed 
film leader and the zone V for the films you mentioned (I am 
particularly interested in the Acros 100 and Neopan 400 either 135 or 
120 films.)  


Thanks !