Re: some observations (and a question) regarding using the sun as a light source

Keith,

that's a tough one, because the spectrum changes
during the day and the emulsion will have a
characteristic absorption spectrum. So it's not just
total energy. It takes me ages to get development in a
salted print after 3-4pm here in texas, and the sun is
still bright. I'm sure it's because there's no UV in
the light. I'm sure the data are out there (in the
plant ecology literature maybe?), but you'd have to
match it to your process - have it broken down by
wavelength and only count the range that your emulsion
reacted to.

David Barker

--- Keith Gerling <Keith@gumphoto.com> wrote:

> A little while back I mentioned that my old Violux
> light source had bit the
> dust. For two weeks I've been using the sun as a
> light source for gum
> printing. Strange, but even though I often coat and
> dry gum prints
> out-of-doors, I've never before considered actually
> using the sun. This has
> been a challenging task! Surrounded as I am by
> trees, it is often hard to
> find openings that are large enough for long enough
> to expose a print.
>
> I was astonished to learn just how bright the sun
> actually is! Six minutes
> under my fluorescent bulbs equals three minutes
> under my Violux equals about
> 45 seconds under the noonday sun. But the time of
> day causes very extreme
> variances in the amount of light. A minute at noon
> might be 4 minutes at
> 3:00 PM.
>
> A question: Is there some kind of chart I can refer
> to that will provide a
> sort of adjustment factor for the amount of sunlight
> falling at a given
> time? Something that will take into account
> latitude and the date?
>
>
>

        
                
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Received on Mon Aug 9 12:02:36 2004