Capturing an Image

The keys to Eastman's success in making photography a popular leisure-time activity for the masses were his development of roll film and the inexpensive box camera. Although today's cameras are mainly digital, and are far more sophisticated and versatile, the fundamental principles behind capturing an image have not changed.

The Camera

Despite their differences, all cameras contain these five basic elements:

• Lens - A glass or plastic element that collects light and focuses an image for capture.
• Diaphragm - An "aperture" or opening that controls the amount of light entering the camera through the lens. The aperture can be fixed, manually adjusted or automatically controlled. Simple cameras usually have a fixed lens opening. In some cameras, a light-sensitive cell adjusts the opening for varying light conditions. In the most sophisticated cameras, the aperture can be manually adjusted.
• Shutter - A device that determines the length of time film is exposed to light entering the camera. Fast shutters can "freeze" fast-moving objects. In motion picture cameras, a 180-degree shutter spins while the film advances at a rate of 24 frames per second.
• Body - The light-proof housing for the camera mechanism.
• Viewfinder - A lens or frame that allows the photographer to see the content of the picture being taken, either through the lens in single-lens-reflex cameras, or through a separate viewfinder in simple cameras.

In digital cameras, images are recorded using electronic image sensors, rather than chemically enabled films. Image sensors are integrated circuits (IC's) consisting of two main components:

Pixels, or picture elements, are individual tiny sites that convert light to electrons. As more light strikes a pixel, more electrons are collected. The number of pixels in a sensor determines the resolution of the image. A typical consumer camera contains between 7 million to 8 million pixels. Output circuitry moves the electrons from each individual pixel and converts the signal to a voltage. The brighter the light that hits the pixel, the higher the voltage. This voltage is then converted to a digital number, and the image is transmitted to a display or storage device, like a memory card.

KODAK EASYSHARE M883 Zoom Digital Camera.

Once the image is read from the sensor it is stored in the camera's memory, and the camera is ready to take a new image. The stored image can then be previewed on the camera back display, or downloaded to a computer for display or printing.

Types of Sensors

With more than 30 years experience in the design and manufacture of electronic image sensors, Kodak is a world leader in image sensor technology. Today, Kodak supplies high-performance image sensors to applications that range from satellite and medical imaging to digital cameras and machine vision products.

The technology used in Kodak sensors falls into four general categories:

• Full-frame CCD imagers
  Kodak is a recognized world leader in the design and manufacture of full-frame charged-coupled device (CCD) technology for performance imaging markets. Full-frame CCDs are particularly noted for their superior image quality and photographic sensitivity, allowing this class of sensors to deliver great pictures even under the most demanding conditions. With resolutions up to 39 million pixels, Kodak full-frame CCDs are widely used in professional digital still cameras, industrial imaging, film digitizing, microscopy and astronomy.
  
  
• Interline CCD imagers
  Interline CCD image sensors are ideal for real-time and high-speed image capture because they do not require the use of a mechanical shutter. With products ranging from video resolution to 11 million pixels, interline CCDs can be found in applications like video cameras, digital still cameras, surveillance cameras, medical imaging, and industrial inspection.



• Linear imagers
  Capturing a single line of an image at a time, linear CCDs capture an image by being scanned across an item, or by having the item move beneath the sensor. The high speed and resolution available from linear imagers make them excellent selections for desktop scanners, document scanners, metrology and remote-sensing satellites.



• CMOS imagers
  Complimentary Metal Oxide Semiconductor (CMOS) image sensors are an alternative to CCDs. CMOS sensors offer lower power consumption and more on-chip functionality. They are well suited for high volume, portable applications such as cameras for cellular phones, PDAs and some digital cameras.

Recently, Kodak announced a technology advance that will increase sensitivity to light by double or 4X (one or two photographic stops) compared to current sensor designs. The first Kodak sensor to use this technology is expected to be available for sampling in 2008.

How Film Works

Film cameras expose images on sensitized film. When exposed properly, photochemical changes occur in the photographic film. Later special developing and processing techniques reproduce the recorded image as a photographic negative, from which prints can be made. Color-reversal films produce positive images that can be mounted as slides.

Making Film: Art and Science

The two chief parts of photographic film are its base and its light-sensitive emulsion.

• The base is a transparent, flexible sheet on which the emulsions (or layers) are coated. Most camera films use a cellulose acetate base, while sheet films (such as x-ray and graphic arts films) use a polyester film base.
• An emulsion is made up of micro-thin layers of gelatin in which light-sensitive ingredients (salts made from extremely pure silver) are suspended. The make-up of an emulsion determines a film's characteristics -- whether it will produce black-and-white or color images and the amount of light needed for proper exposure (indicated by various film speeds).

In Kodak's early years, film base was made -- and coated with emulsions -- on long glass tables. After drying, the coated sheet was stripped off the table and wound. Today, specialized machines make and coat film base in a continuous-roll process. A constant flow of liquid base material is spread in a highly uniform layer (base is measured in ten-thousandths of an inch) on a large, turning wheel. As the wheel turns, the base dries so it can be separated from the wheel as a sheet. For ease of handling, the base is wound in long rolls, sometimes thousands of feet in length. These are now ready for the sensitizing process, where photographic emulsion is coated onto the base.

Glass tables used in early film manufacturing.

Because emulsion is sensitive to light, most steps in its preparation must be performed in near-total or total darkness. After a batch of emulsion is adjusted for desired photographic characteristics, it is piped to large coating machines. In a continuous operation, rolls of base are unwound and the emulsion is applied one side. A typical emulsion layer is only a few thousandth of an inch thick and must be controlled to very strict tolerances. A typical color film requires 17 or more layers of different emulsions and additional color-forming chemicals.

After the emulsion hardens and dries on the base, the film is slit into rolls, spooled if needed, and packaged in the familiar yellow boxes.

Kodak films are produced to demanding standards. They perform consistently when purchased anywhere in the world, and continue to set performance standards in speed, grain, sharpness and color reproduction.