Evening star., 1925-06-28
TO MAKE BETTER PICTURES
BY FREDERIC J. HASKIN

A film standardZer that will con
tribute materially TO the making of
better pictures is the latest discovery
or development OF the photograph
laboratory Of the Bureau of Standards.
Raymond Davis. the chief of the labo-
ratory, is credited with this achieve
ment in the announcement by the De-
partment Of Commerce today.
The selection OF movie films, camera
plates and printing papers so that
they will be best adapted to the work
in hand is aided by Mr.. Davis in
vention. which is an instrument for
the testing and standardiZing of light
sensitive emulsions. II will be known
as the Davis sensitometer.
The emulsions with which plates,
films and papers are coated vary con-
siderably in speed and contrast and in
sensitiveness to light of different col
ors. All OF these properties affect
the use to which the product can be
put.
A fast plate or film is needed for
recording swiftly moving objects, A
"contrasty" plate for use on cloudy
days. or soft plate for use in very
bright sunshine. Brilliantly colored
objects are rendered best by "a plate
and color filter combination. giving
the same color senSitiVenesS as the
eye, while in photographing distant
mountains or making airplane maps
greater sensitiveness to red is
needed.
The Davis sensitometer, il is eX-
planned will permit of the exact meas
urement of all these factors and the
setting up of standards for them. 1t
is. in effect, an instrument for Civ
ing a precisely known set of exposures
to strip OF the emulsion. and for
making these exposures with a light
of known intensity and color. The
darkness of the exposed strips is
measured by means Of a photometer
to obtain values for plotting curves OF
the densities. From these curves the
speed and other characteristics are
obtained.
A large disc having a multiple of
different apertures cut in it forms the
shutter which gives the graduated ex-
posure The opening is so shaped as
to give a series of exposures varying
by a constant ratio and forming on
the plate a row of small rectangles,
each little darker than the one pre-
ceding 1t.
Motor in Step With Clock.
The disc must be driven at constant
speed, and for this purpose an electric
motor is provided having ingenious
devices to make it run at constant
speed and to keep it in step with a
clock. There is an electric shutter
also which is set to remain open dur
ing one revolution of the disc, so that
short, continuous exposure can be
given. although the disc has been
running for some time and has reach
ed constant speed conditions.
An electric light of carefully meas
ured candlepower is used, together
with a special light filter, so that the
color of light obtained is good ap-
Proclamation of daylight throughout
the spectral range. Other color screens
can be placed in front of it to absorb
any desired range Of wave lengths
and give light of any desired color.
MIR. Davis invention is essentially
an instrument of precision and has to
do with the theory rather than the
practice of photography. 1t is for
laboratory use and the manufacturers
of films, plates, printing papers and
the like are, accordingly, primarily in
terested in it. 1t is stated, however,
that it will be of especial value to
astronomers in their photographing
of stars and other heavenly bodies.
The instrument is the product of
some or 10 years of experimental
work and is a typical example of the
the Bureau of Standards to aid all
| lines of industry. 1t is not patented.
Any one may use 1t, for it is one OF
Uncle Sans contributions to progress
| in photography. The man who devel-
oped it gets his reward solely out of
| the satisfaction there is In accom-
plishing that which he started out to
| do, and in knowing that he has done
something worth while.
The average person. it may be
pointed out, does not realize the
patience, hard work and length OF
time that have been devoted to prac-
[ tically every important step in the
development Of photography. Utiliz-
| ing the effect of light on matter as a
means of picture making was first
| thought of in the last decade OF the
eighteenth century, but the first cam
era image was not secured until
1927, Nioephore Niepce accomplish
/ ing that after 13 years of expert
| menting. However, as that required
an exposure of from seven to eight
hours 1t left much to be desired.
Practical Photography In 1889.
Authorities say that practical pho
Biography was not achieved until 1885
when the labors of Daguerre began
to bear fruit. Even Daguerre's iproc
ess was slow, requiring an exposure
| of minutes, and 1T was 1870 before
| the first sunlight picture of a human
face was made by Prof. John VIII
| liam Draper Of the University Of the
| City of New York.
Ten years later the introduction oi
a practical method Of employing col