[alt-photo] Re: Negative Density

[Richard Knoppow]

----- Original Message ----- 
From: "joe" <jazoti at optonline.net>
To: "The alternative photographic processes mailing list" 
<alt-photo-process-list at lists.altphotolist.org>
Sent: Sunday, November 07, 2010 9:21 AM
Subject: [alt-photo] Negative Density


> Hope you can help.
> Am trying to get negative densities, off of APHS film so I 
> can make kallitypes and cyans.
> Have a spot meter.
> Have a Kodak photographic step tab. #3(believe it the same 
> as a stouffer)
>
> Is this possible? or am I going to have to look for a 
> densitometer.
> thank you
>
> joe azoti

     A decent densitometer is of course best but one can get 
pretty good density estimations by visual comparison to a 
calibrated step wedge provided the two can be side by side. 
While the eye is not good at comparisons of brightness  by 
memory it is very good at matching density or color where 
the two are side by side, in fact, the oil-spot type of 
densitometer works on this principle.
     A spot type exposure meter will work provided it can 
read small enough areas and can be calibrated for density 
against the step wedge. Years ago Weston Instrument made a 
simple densitometer consisiting of a light source and a 
large diameter photocell with a cone-shaped fitting mounted 
on an arm. It had a meter calibrated in density. Any 
exposure meter could be used for this sort of densitometer 
with something like a light table as the light source.
     Because the effective density of negatives is affected 
by the nature of the light source the densitometer source 
should match the type to be used in printing. That is, 
whether it is specular (collimated) or diffuse. Depending on 
the nature of the film densities measured with a collimated 
light source will be higher than those measured with a 
diffuse source. This is called the Callier effect and is the 
reason that diffusion enlargers print with lower contrast 
than condenser ones.
     In any case you can probably get a sufficiently good 
estimate by visual comparison to a calibrated step wedge.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com