From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 05/23/01-06:58:48 AM Z
Tom Ferguson wrote:
> ... Either do a similar test to convince yourself, or go out and happily
> make your filtered "snaps".
Hopefully it should be obvious that the optical quality of any filter
should be better than whatever lens it is used with unless one wishes to
alter the quality of the lens. However, one should also be concerned
with: what does this filter do?
The eye has a certain response to various wavelengths of light
(colors). Some individual's responses can substantially differ. The
characteristic of the illumination provides certain amounts of each
color. Each object will reflect or absorb (or refract, fluoresce or
whatever) characteristic percentages of each color. The eye or film
"records" these colors. Different films will respond differently and
will differ from the eye, and different eyes can differ.
Each film has a characteristic spectral response (percent sensitivity
per color). Each lens will have a characteristic spectral transmission
(percent transmission per color). The spectrum of light that has come
from the object to the lens differs from that going to the film. The
brain tries to do some fancy calculations and adjustments to the light
recorded in the eye. Adjustments can be made when printing the
negative. But, what is important is the final print. How are the
colors presented in the final print?
A filter is a device which alters the various percentages of colors
passing through it in a controlled manner. Theoretically some filters
may be able to match film sensitivity and lens characteristics so as to
record the same response as some individual eye. Although it is highly
unlikely that this match ever occurs. More often the filter is used to
alter
the colors so as to lead to certain desired results in the print.
It is very important that one experiment with particular filters so as
to understand results which are also related to the lens, the film, and
the many aspects of the printing process used. A filter which gives the
desired results with one printing process may totally differ with
another
process.
Those who have made many photographs with filters understand this.
However, for the benefit of others, a study of photographing several
subjects each with several filters and without and then printing with a
particular process can reveal what that filter does with those
conditions, equipment, and printing process. Never assume that a
particular filter will give the results obtained with other conditions,
equipment, or printing processes.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
This archive was generated by hypermail 2b30 : 07/12/01-11:29:40 AM Z CST