Photographic films are plastic sheets used to capture images by exposing the layers of plastic to light for specific periods of time, depending on the quality. They consist of sheets of plastic coated with an emulsion that forms a latent image when exposed to light. 

How Photographic Film Works

The emulsion on film contains light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast, and resolution of the photographic films. When the emulsion is exposed to light, an invisible image is formed. Chemical processes are applied to the film, referred to as developing, and the image becomes visible.

When developing photographic films, colored films require at least three layers of silver salts. Dyes absorb the surface of the silver salts and make the crystals sensitive to the different colors. The blue-sensitive layer is often on top, followed by the green and red layers. In development, the silver salts are converted to metallic silver, and then combine with color coupler chemicals in the film itself or the dyes. After development, the silver is converted back into silver salts during the bleach step and is removed during a fix step, which leaves behind only the formed colored dyes that make the image visible.

When developing black-and-white photographic films, there is usually only one layer of silver salts. When exposed grains are developed, the salts are converted into metallic silver which then blocks light; appearing as the black part of the film in the negative.

Types of Photographic Film

There are three common types of photographic film: print, color reversal film, and black-and-white reversal film.

• Print film, also called negative film, turns into negatives when developed, meaning the colors become inverted. These photographic films require printing by either enlarging them by projection through a lens, or placing them in direct contact as a light shines through onto photographic paper. Photographic films that are print types are available in color or black-and-white.
• Color reversal photographic films, also called slide films, are known as transparencies after being developed and are then viewed through a loupe or projector. These films are typically mounted with plastic or cardboard for projection, also known as slides. They are often used for producing digital sans or color separations for mass-market printing.
• Black-and-white reversal films are less common than print and color reversal films. They take conventional black-and-white stock and reverse-process it to result in black-and-white slides.

Selecting the Right Film

Selecting the proper film depends largely on the resources available and the type of pictures being taken. Things to consider include exposure tolerance, film speed, film color, and development locations.

• Exposure tolerance is a film's tolerance for over-exposure to light. Print films can tolerate more over-exposure than reversal films. Reversal films will require some test pictures or rolls to adjust exposure levels correctly. Cameras with few or no manual settings are not suited to use reversal film.
• Film speed is the sensitivity a film has to light. "Faster" films will capture light more quickly than "slower films, decreasing the required exposure and making pictures in lower lighting conditions easier to take. The tradeoff to high film speed is grainier or less clear pictures. Slower film speeds tend to produce more defined pictures, but because the shutter is open longer, lower light and moving environments are much more difficult to capture.
• Film color determines what hues will develop from a picture. Super-saturated color films may be better suited for landscapes and more subtle color schemes better suited for people. The color quality of print film will depend much more however on how the film is developed than on the film selection itself.
• Development locations are much more available for print films than for reversal films, making them much more convenient for everyday use. Reversal films and black-and-white films generally require submission to a professional lab for developing.