From: Marco Pauck (marco@pauck.de)
Date: 06/03/01-03:32:54 PM Z
heather hyatt wrote:
>
> marc,
> > thanks for the help. my normal exposure is about 8
> secs. i took the filter into account. it isn't a
> problem with the exposure but more with a bit of blur.
> i think perhaps that since pinholes are kind of fuzzy
> and IR is sort of fuzzy too that might be the
> problem.
> i have stock piled Kodak HSI, it is too bad they
> stopped making it.
This is getting a little off-topic (well, not quite uncommon
for this list ;-) but let me clarify this:
I was not arguing about the exposure time but the diameter of
the pinhole. The optimal diameter is a function of the distance
to the film plane (the 'focal length') and the light's wavelength.
Therefore, a hole that works perfectly for visible light will be
sub-optimal for IR and vice versa resulting is more than usual blur.
I'm not sure what you mean with "fuzzy", but IR is not more or less
fuzzy than other wavelengths.
Marco
> > Note that IR has a longer wavelength than visible
> > light
> > (depending on the filter you've used, maybe nearly
> > two times).
> >
> > You have to take this into account when computing
> > the
> > appropriate diameter of your pinhole.
> >
> > BTW: Kodak HSI went out of production recently ...
> > :-(
> > The only other 4x5 IR film available now is Maco
> > IR820c.
> >
> > Marco
-- Marco Pauck -- marco@pauck.de -- http://www.pauck.de/marco/ For every complex problem, there is a solution that is simple, neat, and wrong. -- H. L. Mencken
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