Light and Reflection
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
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
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
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
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.
Other Critical Parts of the Camera
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.
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