American Cinematographer - August 2019 - 18

while maintaining the desired depth of
focus and color rendition.
These filters are the Wratten light
filters, No. 96, and bear the catalogue
nomenclature of "No. 96, Neutral Gray."
For all practical purposes it will be
sufficiently correct to compute the density
of this filter as corresponding to a transparency of 1 divided by 12, so that it is
seen that this filter transmits 1⁄12 of the
incident light, or approximately 8%.
Since these filters may be procured
of any desired density, the American Society of Cinematographers has chosen the
following range of densities as the most
appropriate for cinematographic work:
* Density .15 which transmits 66% of
the incident light
* Density .30 which transmits 50% of
the incident light
* Density .45 which transmits 33% of
the incident light
* Density .60 which transmits 25% of
the incident light
* Density .75 which transmits 16% of
the incident light
* Density .90 which transmits 12.5%
of the incident light
* Density 1.05 which transmits 9% of
the incident light
* Density 1.20 which transmits 6% of
the incident light
It is to be noted that the alternate
series, the different densities of which are
.30, .60, .90 and 1.2, bear to each other
the relation that each filter requires
double the exposure of the preceding one,
in other words they correspond to the
regular progression of diaphragm stops.
For example, suppose a scene
which would be correctly exposed when
photographed without a filter at an aperture of F.11.3. The use of the filter density
.30 would require an exposure double the

18

August 2019

one obtained by the aperture F.11.3,
that is to say that the scene should be
photographed at an aperture of F.8.
It is very probable that for normal
cinematographic work it will be sufficient to add only three or four of these
filters to the equipment of the cinematographer, and experience will
dictate the most appropriate densities,
but whenever trick or special process
cinematography is involved, the whole
series selected will present a greater
range of possible effects and therefore a
greater pliability and latitude in the solution of photographic problems.
The color rendition of the subject
is not affected by these natural filters
because they totally absorb only rays
which do not concur to form the image
being absorbed by the glass of the
lenses (wave length 320 mu) and by the
color correcting filters mostly used.
These neutral filters are additive
so the sum of the densities of two filters
gives a very approximate value of the
resultant density when the two filters
are superimposed, consequently they
may also be used in conjunction with
the usual filters used for color correction.
The American Society of Cinematographers is at present discussing
with the Eastman Co., manufacturers of
the neutral filter, the matter of the practical nomenclature to be adopted for
them.
The designation of the filters by
their density involve a certain calculation for the finding of their transparency
and therefore of the exposure they
control; which result impractical when
under pressure of time in actual production work. The most logical manner to
avoid such complication would perhaps

ASC 100th Anniversary

be to add to the trade name and
number the filter factor for each filter,
and to all appearance this will be the
procedure which will be resorted to.
Information for Amateurs
AC Sept. '29

Question from R.S., Mason, Ga.: I
want to try some of the backlighting
effects I see in professional films, but
the instruction books say never make a
picture except where the light comes
over your shoulder. Is there any special
device that studio cinematographers
use to get these effects?
Ans: You can get the effects you
want with any amateur camera if it is
equipped with a lens-hood, or
sunshade, and care is taken that the
direct rays of the sun do not strike the
actual lens surface. In backlit shots, the
light should come from behind and to
the side of the subject, and the best
results are gotten when the sun is fairly
high in the sky. Of course, you should
use some sort of reflector to illuminate
the shadowed side, so the detail there
won't be lost.
Amateur Movie Making
"Some Light on Light"
AC Oct. '29

Light, we know, comes from all
incandescent or burning bodies, and is
reflected by all others. Now light itself is
an electromagnetic wave-motion in the
ether. These light-waves are much the
same as radio waves, but they are
broadcast on a shorter wavelength and
at a tremendously higher frequency.
Instead of measuring their wavelength
in meters, we measure it in ten-thou-
American Cinematographer - August 2019

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