Re: Flashing: was: Making sense of film curve graphs

> > ----- Original Message ----- From: Kate Mahoney
> > To: pinhole-discussion@spitbite.org
> >
> > ............. like burning-in, it can be done either before or
> > after the main exposure. There really shouldn't be any difference!

----- Original Message -----
From: "Wolfgang Thoma" <taco@thoma.be>
>
> I don't have the book and therefore theoretically can not answer, but
> maybe Adams just was afraid to spoil shots with post-flashing that he
> made with his zone system?
> taco

I don't think AA was afraid of spoiling shots, after all he used post
exposure techniques like N+ and N- developments and negative
intensification. He may even have used negative reducers, the man was
fearless :-)

I believe that the reasons the motion picture flashes film is not
necessarily the same reasons still photographers do the same (at least not
all the time). A still photographer usually flashes film to increase the
treshold sensitivity of the film, allowing the film to record detail in the
shadows that otherwise may not be present in the negative. The idea is to
flash the film in such a way that the high zones are virtually unaffected.
By reading Kodak's article, I get the idea that motion picture people is not
primarily interested in shadow details, but in lowering the contrast of the
film, and judging by the curve in the section "flashing camera film", the
contrast of reversal film. They actually say:

" This fairly common practice is often used to create a closer match of two
films' contrast characteristics when they are intercut. It is also used if
the print contrast of a projection contrast reversal camera film is deemed
too high after being printed. "

They do mention: " Lower contrast allows for more detail in shadow areas",
but they say it almost like saying that it is a good side effect of the
flashing technique, but for stills, that is usually the prime effect we are
after.

Having made no tests myself, I can not say categorically, but I am inclined
to think that pre and post flashing may not give the same results all the
time. The idea of exposing film to photons is to flip its grains to a
developable latent state, unfortunately as the photons do the "flipping",
thermal energy tries to undo it. The idea of flashing is to "brake the film
inertia" so when photons from low light levels arrive they accumulate and
not have to "waste" some of them to brake the inertia, first. If you were
to push a heavy loaded truck w/o being able to move it at all, and if you
then move aside and have couple of strong men pushing it and actually
getting it moving, whatever amount of push you did have no effect on what
the string men were capable of doing. That is post exposure, or rather post
pushing!. If on the other hand the 2 strong men push the truck first and
get it moving, braking its inertia, and them they move aside and you keep
pushing you will then be able to keep it moving, this is pre-pushing!!

In any case, if time and the situation allows, pre-flashing would be my
option, otherwise, post-flashing is the next best thing.

_______________________________________________
Post to the list as PLAIN TEXT only - no HTML
pinhole-discussion mailing list
pinhole-discussion@spitbite.org
FAQ at http://spitbite.org/pinhole-discussion/list.html
Received on Tue Nov 30 17:24:54 2004