How Does a Camera Take a Picture?
When we look upon the surface of a mirror we see the image of ourself
and our surroundings. The extent of the view depends upon the size of
the mirror and the distance we are standing from it.
If we hold the mirror close to our face we see only the face, or
perhaps but a portion of it, and the farther away we are the more
the mirror will reflect, only, of course, the various images will be
smaller. The mirror reflecting exactly what the eye sees, without doubt
had a great influence in inducing the experiments that resulted in the
process we call photography.
The taking of a photograph with a camera may in a way be compared
with the action of your eyes, when you gaze upon your reflection in a
mirror, or look at any object or view. Any object in a light strong
enough to render it visible will reflect rays of light from every point.
Now, the eye contains a lens very similar in form to that used in a
camera. This lens collects the rays of light reflected from the object
looked at and brings them to a focus in the back of the eye, forming an
image or picture of whatever we see, just as the mirror collects the
rays of light and reflects them back through the lens of the eye.
Certain nerves transmit the impression of the image so focused in the
back of the eye to the brain and we experience the sensation of sight.
What Is the Eye of the Camera?
The lens is the eye of the camera, and the process we call photography
is the method employed to make permanent the image the eye or lens of
the camera presents to a sensitive surface within the camera.
Fig. 1 shows a simple form of camera, it being merely a light tight box
with a lens fitted to the front, and a means for holding a sensitive
plate at the back, the plate being placed at just the right distance to
focus the rays of light admitted through the lens in exactly the same
manner as the rays of light pass through the lens of the eye and come
to a focus in the back part of the eye.
Now, if we could look inside the camera we would note that the image
was inverted, or upside down.
Fig. 2 will explain this.
The rays of light from “A” pass in a straight line through the lens
“B” until they are interrupted by “C,” upon which they strike, forming
an upside down image of the object “A.” But, you exclaim, “we do not
see things upside down.” No, we do not, because some mental process
readjusts this during the passing of the impression from the eye to our
brain.
Let us suppose we have our camera loaded with its sensitive plate or
film. We select some object or view we wish to photograph, uncover
the lens for an instant, and let the light impress the image upon the
sensitive surface of the plate or film. Now, how are we going to make
this image permanent?
If we were to examine the creamy yellow strip of film upon which the
picture was taken there would seemingly be no difference between its
present appearance and before the snapshot was made.
Now let us suppose that this strip of film is a little trundle bed, and
in it tucked securely away from the light are many hundreds of little
chaps called silver bromides, little roly-poly fellows lying just as
close together as possible, and protected by a coverlet of pure white
gelatine.
~HOW A PHOTOGRAPH IS DEVELOPED~
Until the sudden flash of light in their faces when the picture was
taken, they have been content to lie still and sleep soundly. Now
they are seized with a strange unrest, and each little atom is eager
to do his part in showing your picture to the world. Alone they are
powerless, but they have, all unbeknown to them, some powerful chemical
friends, who, organized and aided by the photographer, will bring
about their transformation. These chemicals, with the help of the
photographer, form themselves into a society called the developer.
The photographer takes just so many of the tiny feathery crystals of
pyro, just so many of the clear little atoms of sulphite of soda, and
just so many little crystals of carbonate of soda, and tumbles them
all into a beaker of clear cold water. Unaided by each other, any one
of these chemicals would be powerless to help their little bromide
of silver friends. The first of these chemicals to go to work is the
carbonate of soda.
He tiptoes softly over to the trundle bed and gently begins turning
back the gelatine covers over the little bromide of silver chaps, so
that Pyro can find them in the dark.
It is Pyro’s mission to transform the little silver bromides into
silver metal, but he is rather an impulsive chap, so he is accompanied
by sulphite of soda, who warns him not to be too rough, and whose sole
mission is to strain his eagerness to help his friends.
“Go slow now,” says Sulphite, “don’t frighten the little silver
bromides, or else you’ll make them cuddle up in heaps, and the picture
won’t be as nice as if you wake them up gently and each little bromide
stayed just where he belonged.”
After all the little silver bromides that the light shone on have been
transformed into metallic silver by the developer, another chemical
friend has to step in and carry away all the little bromides that were
not awakened by the flash of light.
This friend’s name is “Hypo,” and in a few minutes he has carried away
all the little bromides that are still sleeping, so that the trundle
bed with the now awakened and transformed silver bromides will, after
washing and drying, be called a negative, and ready to print your
pictures from.
If we take this negative, as it is called, and hold it up to the
light, we will see that everything is reversed, not only from right to
left, but also that whatever is white or light in color is dark in the
negative, and that what would correspond to the darker parts of our
picture are the lightest in the negative, and it is from these facts
that we give it the name negative.
Now, to get our picture as it should be, we must place this negative in
contact with a sheet of coated paper that is also sensitive to light.
So we place the negative and the sheet of sensitive paper in what is
called a printing frame, with the negative uppermost, so that the light
may shine through the negative, and impress the image upon the sheet of
sensitive paper. Now, it stands to reason that if the lightest parts of
our picture are the darkest in the negative that less light can pass
through such portions of the negative in a given time, so that with the
proper exposure to light the image upon the sheet of sensitive paper
will be a correct picture of whatever the lens saw.
[Illustration: The swiftest thing that the human race has ever put into
motion is the steel projectile of a twelve-inch gun. No human eye can
follow its flight. Released at a pressure of forty thousand pounds to
the square inch--in a heat at which diamonds melt and carbon boils--it
hurls through the air at the rate of twenty-five miles a minute, and
reaches the mark _ahead of its own sound_! (Pictures and story by
courtesy of McClure’s Magazine.)]