Re: Flashing before or after exposure...

Eric wrote:
> George wrote:
> > As I see it, it is additive no matter which way you go. I would
> > imagine that an exposure could decrease the threshold in certain
> > areas, then a post flashing could trigger these grain clusters.
> > Testing is the only way to know for sure, but since I do not have
> > a densitometer I would need to yield this to someone with the
> > proper equipment. I am going to guess that one will not be able
> > to tell the difference through observation, just as I am not able
> > to tell the difference between a "perfect" pinhole and one that is
> > slightly too large or small.
> >
> > When I get a chance I will see if the above is correct. I have a
> > decent supply of Panalure and will be testing some of this anyway.
>
> You do not need a densitometer; you can use an exposure meter, as
> out lined in a book I got out from the library[some time
> ago]. Admittedly this was for negatives using an enlarger if you are
> interested will get details, and mail them to you

The book is Phill Davis' "Beyond the Zone System". He has
instructions in an appendix explaining how to use a spot meter (with
1/10 stop readout) and a closeup lens as a densitometer (either
transmission or reflection). You need an appropriate step tablet in
order to calibrate your light source.

You could also do this with a scanner and a step tablet. Turn off all
color management and measure each of the steps using the eyedropper
tool in the scanner software (without saving the file). Then you can
compare with your negative (also in the scanner software).

Bob Wheeler <URL:http://www.bobwheeler.com/> has an article on his
site describing using a scanner as a densitometer.

<URL:http://www.bobwheeler.com/photo/Documents/ZoneDigital.pdf>

As far as pre-flashing vs. post-flashing goes, I'm pretty sure that
they are equivalent. The idea is that the flash exposes the film or
paper to a level just below what would show up after processing. If
you do it pre-exposure then during the exposure the very dark shadows
will add with the existing pre-flash exposure to become visible after
processing. If you do it post-exposure the flashing will push shadow
values that are not visible up to the visible range.

-- 
Brian Reynolds                  | "It's just like flying a spaceship.
reynolds@panix.com              |  You push some buttons and see
http://www.panix.com/~reynolds/ |  what happens." -- Zapp Brannigan
NAR# 54438                      |  
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