[alt-photo] Re: Negative Density

[Jacques Kevers]

Years ago, the Gossen Profisix meter had an accessory that originally was
intended for taking measures on the ground glass of view cameras: the
"Profi-Flex" that could be used as kind of a densitometer.
See
http://www.butkus.org/chinon/flashes_meters/gossen_profi-flex/gossen_profi-flex.htm
The remarks about light source characteristics are completely justified, of
course...
Best,
Jacques

2010/11/7 Richard Knoppow <dickburk at ix.netcom.com>

>    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.
>