Evening star., 1949-11-13
Camera Angles
The Proper Use of Corrective Filters
" Alexander J. Wedderburn
curotor Of Photography
Iha Sn,ifhs nninn lns sfifution


The Smithsonian institution
There are many uses for filters
in photography. You will un-
doubtedly be able to improve your
pictures if you use them for their
designed purposes. But if you don't
know the why's and wherefores
of filters it will be best to leave
them strictly alone. for just any
old filter slipped over your lens
will just as surely upset your plans
and spoil your negatives.
Most amateurs think of a filter
as a gadget designed to help us
record clouds. But too often a be-
ginner will get hold of the wrong
type of filter, use it, and then
wonder why his film came back
from the photofinisher with moth
ing on it or so badly underexposed
as to be worthless for printing
purposes.
Right away it should be under
stood that every time a filter is
used In taking a photograph some
thing is subtracted or taken away,
for filters are designed to absorb
a portion of the light reflected by
the subject. What and how much
is taken away or absorbed from
the light reflected from the sub
ject depends on the color and den-
Sity of the filter as well as the tvpe
of film used.
In the first place. we shall have
to consider the makeup or white"
light or sunlight which we use in
the exposure of negatives. AL
though this so-called white light
appears white" actually it is
composed of a mixture of all the
colors of the spectrum. In school
we have all seen proof of this in
experiments where a beam of light |
is passed through a prism and up
on emerging, is broken down into
the colors of the rainbow.
Black and White Rendition. /
These light primary" colors
are blue, red and green. Along
with these you will have noted
many of their combinations such I
as violet. yellow. red, orange,
blue-green and others. Now, as
we all know, objects appear to our
eyes as having certain definite
colors. On film these colors are
interpreted as various shades run
ming from white. and through the
middle tones of gray, to black. i
And therein lies the substance of !
our problem.
. Films, not having the same de-
gree OF selectivity as the human
eye, cannot "see" colors in the
same way. AS result, degrees Of
color brightness as interpreted by
the eye are not similarly recorded
by film with any accurate degree
of faithful rendition. To over
come this situation, we have come
to reply on filters as a means by
which we may approximate on
film. in terms Of black and white,
the relative values of the differ
ent colors of the spectrum.
A moment back we discussed
the basic or primary colors Of
light-red. blue and green. And
we know that these colors or
combinations thereof determine
the appearance in terms of color
of all objects with which they
come in contact by means of light !
transmission. Now let's go a step
further. Objects do not neces-
sarily reflect all light falling on
them. On the contrary. much of
the light is absorbed. Then it |
naturally follows that the color
Of an object, as we see it, depends
upon which of the colors it alb
serbs and which are reflected.
Color Is Reflected.
AS an example. take red paint. |
Red paint is not red. 1t merely
appears red to us because it has
the physical quality to absorb the
blue and green. It does not alb
sorb the red which is reflected to |
our eyes and thus we see red
paint as red" The same prin-
ciple applies to all other colors.
Some objects have this quality to
absorb all Of one or more of the
basic or primary colors while
others only absorb a portion. This
is why we see colors other than
the primaries-such as orange,
yellow. blue-green, etc.
Orthochromatic film and pam
chromatic film react differently to
the light of different colors. AS
case in point, ortho film does not
record the color of red at all. Nor
do all panchromatic films respond
identically to the light of differ
ent colors. Some are more sensi-
tive to red than others. There
fore it becomes apparent that we
shall have to take some step to
reconcile these differences so that
the picture on film will look as
nearly as possible as the scene
we looked upon with the various
colors interpreted in terms of the
gray scale. This is where the FL
ter comes in.
In taking a landscape shot
without a filter you will have no
ticed that the film was highly +
sensitive to the blue of the sky
and consequently any clouds were
"lost." Now il. yellow filter is
placed over the lens it will alb
sorb to very great extent any
blue reflected light leaving the
cloud formations as you saw them
with your eyes. But If a blue fl