From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 05/24/01-07:10:20 AM Z
Steve Shapiro wrote:
> ... It is that latter one that can
> help in deep canyons or valleys, and making the sky dark.
Part of my point is that one must be cautious with generalities on the
use of filters, especially between processes. For example, a yellow or
orange filter that provides the desired effect with gelatin silver may
be too harsh for Pt/Pd. It such a case perhaps a light yellow or no
filter would produce a more desirable result. The Pt/Pd process has
much more the ability to discriminate subtle tone values.
Another consideration is that a process such as gelatin silver renders a
large dynamic tonal range "dark sky" type image much better than Pt/Pd.
It makes sense that one would choose their process to accommodate their
desired results, and this will also have an impact on their use of
filters.
Personally I like to discriminate tones rather than separate them.
Although there have been a few instances when I used a filter and even
lowered the value of the sky a bit. But "dark sky" type images are not
my preference. I always carry some gel filters as they are light in
weight and one never knows when they may be useful.
One example that comes to mind is my folding screen of the Hayden Flour
Mill (one of the examples on my web site, at this link:
http://home.att.net/~jeffrey.d.mathias/folding_screens.htm
This photograph was made from three dramatically different camera
positions, with the dark structure on the left and right being the same
photographed from different sides. A problem I realized is that the sky
would be dramatically different in value from these three positions
(angles). I used different filters (yellow and a polarizing) so as to
maintain close enough values in the sky and in relation to the silos so
that I could make
smaller adjustments to the highlight masks when building the negatives
so that each panel would print with the same value sky. (Note that the
difference in the sky seen in this E-copy is due to the panels being at
different angles to the illumination.)
Which also leads to something Dan wrote.
FDanB@aol.com wrote:
> ... Since the image is going to be digitized at some point anyway, the
> color tools in Photoshop provide much finer control than that of physical
> filters used over the lens in the field.
> ...
> In fact, the polarizer is about the only filter whose effect can't be
> duplicated in the digital lightroom.
One should keep in mind that the film or sensor array is limited to a
certain range or response. The original information is limited to what
has been captured. So enough information must be present so as to be
able to subtract from it. As with my folding screen mentioned above, I
could have altered the sky entirely with the mask. However, this would
have required more dramatic alterations than incorporating the use of
the filters. Would the results have been the same, I do not know, but
do feel it would have been more difficult.
Think also of adjusting color balance. A color balancing filter usually
requires more exposure. This assures that enough information is stored
in the original at the corrected color balance. Without this
information (without the filter), the digital control may not be able to
retain enough original signal of certain parts of the spectrum when
subtracting to perform the color balance.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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