A fully manual single-lens-reflex camera..
Photography is undoubtedly one of the most important inventions in history
-- it has truly transformed how people conceive of the world. Now we can
"see" all sorts of things that are actually many miles -- and years
-- away from us. Photography lets us capture moments in time and preserve them
for years to come.The basic technology that makes all of this possible is fairly simple. A still film camera is made of three basic elements: an optical element (the lens), a chemical element (the film) and a mechanical element (the camera body itself). As we'll see, the only trick to photography is calibrating and combining these elements in such a way that they record a crisp, recognizable image.
There are many different ways of bringing everything together. In this article, we'll look at a manual single-lens-reflex (SLR) camera. This is a camera where the photographer sees exactly the same image that is exposed to the film and can adjust everything by turning dials and clicking buttons. Since it doesn't need any electricity to take a picture, a manual SLR camera provides an excellent illustration of the fundamental processes of photography.
The optical component of the camera is the lens. At its simplest, a lens is just a curved piece of glass or plastic. Its job is to take the beams of light bouncing off of an object and redirect them so they come together to form a real image -- an image that looks just like the scene in front of the lens.
But how can a piece of glass do this? The process is actually very simple. As light travels from one medium to another, it changes speed. Light travels more quickly through air than it does through glass, so a lens slows it down.
When light waves enter a piece of glass at an angle, one part of the wave will reach the glass before another and so will start slowing down first. This is something like pushing a shopping cart from pavement to grass, at an angle. The right wheel hits the grass first and so slows down while the left wheel is still on the pavement. Because the left wheel is briefly moving more quickly than the right wheel, the shopping cart turns to the right as it moves onto the grass.
How Does a Camera Work?
Other People Are Reading
1. Light and Reflection
o
As light bounces off an object, it reflects the
image of that object, which is the basic principle that all cameras rely on to
capture images. When you hold a camera in front of your subject, to take a
picture or movie, the light reflects from the scene, and strikes the lens of
the camera, then forms an inverted or upside down image on the far inside wall
of the camera. Another way to illustrate this concept would be to stand in a
small, dark, windowless room during daylight. If you were to make a small
pinhole into the center of the outside wall, light would stream into the room.
The image of the outside scene beyond the wall would be projected onto the back
wall. Yet, it would be upside down.
The First Camera
o
The word "camera" evolves from the
Latin term meaning "dark chamber." Centuries before the invention of
photography the first camera was being used by artists as a device to assist in
sketching large objects. This was called a camera obscura. The camera obscura
was a box, and inside a mirror was set at a 45 degree angle to reflect the
image that streamed into the aperture, up to a glass screen on the top of the
box, which was where the artist could then trace the image.
Lenses
o
Lenses were used, even in the earliest cameras,
to focus or improve the clarity of the reflection streaming into the camera.
Another factor that controls the sharpness of the image is the size of the
opening that lets in the light. The smaller the aperture, the sharper the
image. This is a principle modern day photographers use to control the quality
of their photographs. If there isn't adequate lighting to take a picture, the
photographer might increase the aperture size, letting in more light. In doing
so, the range of focus will diminish.
Light Sensitive Chemicals
o
Prior to the invention of modern photography,
scientists were experimenting with light sensitive materials, in hopes of
capturing the image that was projected onto the back wall of the camera.
Different techniques were developed over time, including the Daguerreotype that
used sheets of silver coated copper, and an invention by William Talbot that
used light-sensitive paper.
Shutters
o
Cameras have shutters that open to let in light.
The speed of the shutter is another way photographers control the quality of
their pictures. If a photographer wants to take a picture of a moving object,
without the object blurring, they choose a fast shutter speed. But if the
lighting is poor, they may need a slower shutter speed, to let in more light.
Another option would be to use films that require less light, though those
often produce grainier images.
1. Other Critical Parts of the Camera
o
A diaphragm is a device that expands to let in
more light. It is fitted near the camera lens, and some cameras have automatic
mechanisms that adjust the diaphragm. And a viewfinder is the device on the
camera that allows the photographer to see what the camera is seeing.
1. Anatomy of a Camera
o
The
parts of the simplest possible camera are a dark box with a small hole or
window and some photographic medium on the inside back wall for recording the
image. For everyday cameras, the dark box is replaced by a camera body. The
window--technically called the aperture--is covered with a ground-glass lens
for focusing the light that enters the camera. Between the lens and the window
is a shutter that opens to let light into the camera body. The photographic
medium is the film on which the light image is recorded.
2. Light Is Focused by the Camera Lens
o
The shape of the lens
determines how light will be focused. Some lenses are designed to focus on
far-away objects. Other lenses are shaped to focus on close objects. Precise
focusing is done by moving the lens closer to, or father from, the camera.
3. The Aperture Controls How Much Light Passes Into the Camera
o
A large
aperture allows a lot of light to enter the camera and is good for low-light
photography. But a large aperture also diminishes the range of focus, so the
photographer must be precise in focusing. A small aperture lets less light into
the camera, and is good for bright-light photography. A small aperture also broadens
the range of focus so that the photographer has a greater margin of error in
focusing. The aperture on most cameras can be adjusted so you get the best
light exposure for your photograph.
4. The Shutter Controls How Long Light Is Allowed to Pass Into the Camera
o
The
shutter opens briefly when you depress the camera shutter button The amount of
time the shutter stays open is called the shutter speed. A faster shutter speed
lets less light into the camera. Fast shutter speeds are good for action
photography and bright-light photography. Slow shutter speeds are good for
still life or low-light photography.
5. The Light Image is Captured on Film
o
While the shutter is
open, the camera lens focuses light on the film at the back of the camera. The
film reacts chemically to the light so that the image is recorded. A lever on
the camera advances the film frame by frame until the entire roll of film is
exposed. If the film is exposed to additional light after images are recorded,
the original images will be obscured. This is why film is enclosed in
light-proof cartridges until it is developed.
Developing Makes Film Stop Reacting to Light
o
Once the film has been
exposed in the camera, it is rewound into its cartridge and removed for
developing. Developing involves removing the film from the cartridge and
exposing it to chemicals that stop the film from reacting to further light
exposure. This process is done in complete darkness. Once the film is
developed, it can safely be exposed to light and is ready for making
photographic prints.
No comments:
Post a Comment