Re: [APML] Preflash film with colored light?

["Don Westergren" <westergren@netzero.net>]

Gil,

The film manufacturer's film data sheets have the Spectral-Sensitivity
curves that show the relative sensitivity for a range of light wavelengths.
You can find them (usually pdf files) by digging through the film web sites.
I doubt you will find any color films that go out to 700 nm.  We have been
searching for any films that have response at H-Alpha at 656 nm.  In the
past few years, all the color negative films have been adjusted to cut-off
at shorter than 656 "in order to give proper skin tones" and "more realistic
pictures of red roses".

To flash film for the H-Alpha red light, you need red light at 656 nm.  I
found an LED (276-309) at Radio Shack a few years ago that peaks at 656,
ranging above it's half power output from about 630 to 670 nm (measured with
two separate spectrometers).  I can't guarantee that all of those stock LEDs
have the same light output.  I checked several blue LEDs and found their
peaks ranged over 20 nm.

Good Luck,
Don

> I want to test this out too, how do I find out if the
> film is sensitive to 700nm or so?  Is it in Kodak and
> Fuji's technical papers?
>
> - Gil
>
> --- George Anderson <georgea@cam.org> wrote:
>
> > Hi Gil
> >
> > It is one of the things on my to do list if we ever
> > get any clear skies
> > without a moon. I have two B&W films to finish
> > testing and then I want
> > to have a shot at one of the colour films that has a
> > weak red response
> > due to reciprocity failure.
> > The film has to extend beyond 650nm to start with
> > otherwise it is a lost
> > cause. If there is no sensitivity at that wavelength
> > then preflashing
> > won't do a thing for the film as far as catching
> > H-Alpha light.
> > The idea is to bump the red "fog" level up to where
> > the exposure is more
> > colour balanced and hopefully keep more of the red
> > photons which strike
> > the film rather than have them bleed off due to an
> > insufficient number
> > striking the film grains.
> > BUT, the whole idea is theoretical and may bear no
> > fruit other than to
> > create other problems with the negative.
> > At the current rate of shooting days I may get a
> > chance to try this out
> > in November.
> >
> > George Anderson
> > Montreal Canada
> >
> > Clear skies and good health
> >
> > Gil McFarlane wrote:
> > >
> > > Has anyone experimented with preflashing color
> > > negative film with red light to see if it improves
> > the
> > > film's red responsivity?
> > >
> > > - Gil
> > >
> > >
>
>
>
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