[alt-photo] Re: pd/pt coating solutions

[etienne garbaux]

francis wrote:

>I feel there is a gap in my alternative processes knowledge regarding
>exposure scale. Would someone point me towards some reading either online or
>an alt processes book?

ES is simply the variation in exposure required to obtain the full 
range of densities on a given medium.  Usually expressed in stops, or 
sometimes in the number of wedge steps (in that case, one needs to 
specify the step size of the wedge).  It is an INPUT FUNCTION of a medium.

Density Range ("DR") is the range of densities (either reflection 
density, in the case of opaque media, or transmission density, in the 
case of transparent media) that a given medium will produce -- i.e., 
Dmax minus Dmin.  DR is generally expressed in log Density.  (DR is 
also used to express the range of densities in a particular negative 
or print, which may not contain values from Dmin to Dmax.)  It is an 
OUTPUT FUNCTION of a medium.

If the DR of a negative medium is the same as the ES of the printing 
medium, then a full-range negative (i.e., one containing densities 
from Dmin to Dmax) will create a full-range print.

Note that the ES of a medium and its DR are rarely related 1:1 -- 
most media either compress values (i.e., low contrast media where 
ES > DR) or expand them (i.e., high contrast media where ES < DR).

It is not uncommon to see these terms confused.

Best regards,

etienne