Re: exposure time

From: henk thijs <henk.thijs@hetnet.nl>
Subject: exposure time
Date: Wed, 05 Jan 2005 20:25:01 +0100

> I had to double the distance of my UV-source to the neg and applied
> the rule I used working with my enlarger with silver-gelatine
> printing: 2times the distance , 4 times the exposure time , that
> idea.
> I did the same with my gum-printing but had problems with clearing.
> Is there a different treatment for UV and 'normal' light exposure? Or
> is it the normal 'alt-process-unpredictable-do-it-yourself-procedure'
> rule?

That inverse square law works if the light source can be approximated
as a point source. If the source has a fairly large aperture (e.g.,
reflector and diffuser), and the distance is not too large, which I
suppose is your case, the light shouldn't fall off as much as what the
inverse square law predicts. But there is no analytical (mathematical)
relation you can use without doing actual measurement.

As the distance becomes very large, any finite aperture can be
reasonably approximated as a point source and you can use inverse
square law again.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)