Photography

A commercial camera based on Daguerre's patent, came out in France in 1839. New camera designs followed, mirroring the changing uses for and technologies used in photography. Large portrait cameras, small, foldable cameras for portable use, and twin-lensed cameras for stereoscope photos came out soon after the invention of photography. Bellows cameras allowed photographers to precisely control the focus and perspective of images by moving the front and back ends of a camera, and thus the focal planes.

The single lens reflex camera, which allowed for great control over focus and a fast exposure time, was an important advance that lead toward today's cameras. This camera used a mirror, usually set at a 45 degree angle to the lens, to allow photographers to look directly through the lens and see what the film would "see." When the shutter opened, the mirror moved out of the way, causing the image to reach the film rather than the photographers eye. Single lens reflex cameras were in use by the 1860s, and used roll film by the 1890s. Because they were easy to use and allowed for a great degree of spontaneity, this type of camera proved popular with photojournalists, naturalists, and portrait photographers.

In early photography, exposures were made by simply taking off and replacing the lens cap. With the introduction of dry plates and film that were more sensitive to light, photographers required a more precise way of making fast exposures, and shutters became necessary. By 1900, shutters were sophisticated enough to all control of the aperture size and shutter speeds, which generally went from one second to 1/100th of a second. Lenses were improved to allow larger apertures without a loss of focus resolution. With exposure times becoming more precise, methods of precisely measuring light intensity became important. Initially, a strip of light-sensitive paper was used, then pieces of specially treated glass. The most accurate method used selenium, a light-sensitive element. Photoelectric meters based on selenium were introduced in 1932. They became smaller and less expensive, until by the 1940s, many cameras came with built-in light meters.

Cameras continued to become lighter and smaller throughout the twentieth century. The 35 millimeter roll film camera so widely used today had it's origins in a 1913 Leitz camera designed to use leftover movie film. In 1925 Leitz introduced the Leica 35mm camera, the first to combine speed, versatility, and high image quality with lightness and ease of use. It revolutionized professional and artistic photography, while later models following its basic design did the same for amateur photography. In the years that followed, motor drives that automatically advanced film, and flashes that provided enough light in dark situations were perfected. The flash started in the mid-19th century as a device that burned a puff of magnesium powder. By 1925 it had become the flashbulb, using a magnesium wire. In the 1950s, the invention of the transistor and dry-cell batteries lead to smaller, lighter flashes, and smaller, lighter cameras as well. In all but the simplest cameras, photographic exposures are controlled by two factors: how long the shutter stays open, and the size of the hole in the lens is that admits light into the camera. This hole, called the aperture, is usually measured as a proportion of the distance from the aperture to the film divided by the actual diameter of the aperture.