Evening star. [volume] (Washington, D.C.) 1854-1972, 1948-01-11

of exposure is determined by the
size of the diaphragm aperture. The
and minimum speeds are
indicated on most lenses by so-called
+. stops or numbers. The numbers
serve as guide for controlling the
opening of the iris diaphragm, which
Is a simple arrangement Of series
of thin overlapping metal leaves
contained between the elements OF
the lens. These leaves are attached
at one end to a ring which may be
manually operated to vary the size
of the circular opening between
them, thus controlling the amount
of light reaching the negative. One
most important fact to remember
when setting the diaphragm aper-
ture is that the openings are cali
brated in such a manner as to double
the exposure for given shutter
speed If made larger by one stop.
Conversely, if the opening is made
smaller by one stop, the exposure
will be halved for q given shutter
speed.
Wider Aperture for Speed.
Let's say, for example. that we
have just made an exposure of a
landscape at 1/25th Of a second and
the aperture is set at i'll. Just
about this time, Junior wanders into
what you feel is a perfect setting
for q natural, imposed picture. Be-
cause he is moving about rapidly
with studied unconcern for your
efforts with the camera, 1t becomes
necessary to readjust the aperture
and shutter speed to conform with
his actions. If he Is not racing
about too wildly, the shutter, speed
can be set at 1/50th of q second,
which cuts the exposure time one
half. To compensate for this, the
aperture should be enlarged from
fill to f.s, thus admitting twice the
amount Of light than before. 1t can
readily be seen that, although both
shutter speed and aperture are diff
ferent than in the first exposure,
the two negatives will have the same
relative exposure and will, there
fore, develop evenly in the darkroom.
Had the shutter speed for the second
exposure remained constant at
1/25th of q second, opening the
aperture one full stop would have
caused an overexposure. Had the
aperture remained the same and the
shutter speed doubled, the result
would have been an underexposed
film.
Fortunately the wide latitude of
present-day films covers up multi
tude of sins of omission and COM
mission in the way of poor exposure.
However, this assist from the film
manufacturer cannot be depended
on in the case Of serious mistake.
Eloquent witness of this is the large
number of badly exposed negatives
that pass through the hands Of the
photo finishers every day.
Focal Plane Shutters.
The shutter Of your camera, I'M
less you are using the one that
grandfather stored away, will be one
of the types most commonly found
on cameras today. The better anna
teur cameras have their shutters
located either between the lens ele-
ments or, in some cases, in front of
the Aim. The latter type Is most
frequently seen on press-type cam
eras and is known as q focal plane
shutter. A few cameras have the
shutter installed either in front or
in back of the lens. All are simple
In operation-but. word Of warn
ing-never attempt to take a shut
ter apart for cleaning or for any
other purpose. This is job that
only an experienced camera repair
man understands. ~ '
The final link in the chain of
correct exposure is the amount of
light available to record an image
on the film. Some few photogra-
pliers with many years of expert
ence can Judge exposure correctly
without light meter, but for the
beginner this highly specialized in
Ia a neceSSity.