Photographic film is a thin strip or sheet of flexible plastic coated with a light-sensitive material called emulsion. There are many kinds of film. Film is different in many ways: size, mode, color sensitivity, graininess, speed, and resolution.
Film Size
Film is produced in many different sizes to match different camera formats. Film size refers to the dimensions to which the film has been cut. The most common film size is 35mm.
Film Mode
Film is packaged in three basic modes:
Roll or Film – is the most common. It is packaged in a light tight container called a cassette. Roll film is bought by length or the number of exposures per roll.
Cartridge Film – is a light tight plastic container that drops into cartridge type cameras. Their major advantage was that no film threading was required. Cartridge film is not used much today.
Sheet Film – is used for large format cameras. It must be loaded into film holders in total darkness.
Color Sensitivity
Color sensitivity is the way that film responds to light of various wavelengths (color). Most film is panchromatic or sensitive to all colors of light.
Graininess
Graininess is the sand-like effect that appears when a negative is enlarged. It is a result of the size of the silver grains used in the emulsion. All film has grain and the degree of graininess depends on the type and speed of film used.
Film Speed
Film speed is a measure of a film’s sensitivity to light. Film that is very light sensitive is called fast film. Fast film is used for dimly lit subjects or for fast moving subjects. Film that needs more light to produce a good image is known as slow film. Bright subjects or long exposures are examples of slow film use. Film speed is directly proportional to the size of the silver particles in the emulsion. The larger the particle, the larger the surface area. More surface area translates into a faster exposure time. Film is rated by it’s ASA/ISO number. The higher the number, the faster the film.
Resolution
Resolution is the ability of a film to record fine details. Slow film can produce smaller and finer details than fast speed film.
Parts of Black and White Film
Black and white film is composed of five layers:
super coat – protects the emulsion.
emulsion – silver halides suspended in a gelatin base.
acetate base – plastic layer on which the emulsion is spread.
anti-curl layer – prevents the film from curling.
anti-halation layer – prevents light from being reflected back to the emulsion.
How Film Works
Film reacts when light strikes some of the silver halide crystals during exposure. When exposed to light, a change occurs within the chemical structure of the silver halide crystal. There is no visible change, but a latent image is formed and must be brought out by developing agents. The developer converts the exposed silver halide crystals into black metallic silver, which can be seen. The more light that reaches the emulsion, the more crystals affected. This is the reason that a negative is the reverse of the subject. Light areas reflect more light back to the film. Dark areas on the subject absorb more light and therefore less light is reflected back to the film.
Negatives are not composed of strictly black and clear areas. A negative has many different tones ranging from black to clear.
Density and Contrast
Density describes the light-transmitting qualities of a negative. Density depends on the type of film used and the amount of light striking the film.
Contrast is the difference in densities of the various areas of a negative. Contrast is determined by the type of film used and the contrast in the subject.
Exposure Control
Exposure is the amount of light allowed to fall on the film while the intensity of the light entering the camera is controlled by the aperture. Shutter speed controls the amount of time that the light is allowed to fall on the film.
In simple terms, light of a higher intensity acting for a short period of time will produce the same photographic effect on film as a light of a lesser intensity acting for a longer period of time. This is known as the Law of Reciprocity. The following exposures will allow the same amount of light to reach the film and produce negatives of the same intensity.
1/500 second at f/5.6 1/250 second at f/8 1/125 second at f/11 1/60 second at f/16 1/30 second at f/22
The Film Camera
Film Photography: All film cameras have the same basic parts. You will need to become familiar with these parts and their function.
All film-based cameras have the same basic features:
A light-tight box to hold the camera parts and film.
A viewing system that lets you aim the camera accurately.
A lens to form an image and a mechanism to focus it sharply.
A shutter and lens aperture to control the amount of light that reaches the film.
A means to advance the film.
The Parts
A. Body – The light-tight box that contains the camera’s mechanisms and protects the film from light until you are ready to take the photograph.
B. Lens – Focuses an image in the viewfinder and onto the film.
C.Lens elements – The optical glass lens components that produce the image.
D. Focusing ring – Turning the ring focuses the image by adjusting the distance of the lens from the film plane. Some cameras can focus automatically. Simple cameras have a fixed lens.
E. Diaphragm – A circle of overlapping leaves inside the lens that controls the size f the aperture or lens opening. It opens up to increase or closes down to decrease the amount of light reaching the film.
F. Aperture ring – Setting the ring determines the size of the diaphragm during exposure.
G. Mirror – During viewing, the mirror reflects light from the lens upward onto the viewing screen. During exposure, the mirror swings out of the way so light can pass straight to the film.
H.Viewing Screen – A ground-glass or similar surface on which the focused image appears.
I. Pentaprism – A five sided optical device that reflects the image from the viewing screen into the viewfinder.
J. Metering cell – Measures the brightness of the scene being photographed.
K. Viewfinder eyepiece – A window through which the image from the pentaprism is visible to the photographer.
L. Shutter – Keeps light from the film until you are ready to take a picture. Pressing the shutter release opens and closes the shutter to let a measured amount of light to reach the film.
M. Film – The light-sensitive material that records the image. The film speed (the rating of a particular film’s sensitivity to light) is set into the camera by turning a dial or on some cameras, is set automatically when you load the film.
N. Film advance – A lever that advances the film to the next unexposed segment. Some cameras advance the film automatically.
O. Shutter-speed dial – Selects the shutter speed, the length of time that the shutter stays open.
P. Shutter release – A button that activates the exposure sequence in which the aperture adjusts, the mirror rises, the shutter opens, and light strikes the film.
Q.Flash mounts – A bracket that attaches a flash unit to the camera and provides an electronic linking that synchronizes camera and flash.
R.Rewind mechanism – A crank that rewinds the film into its cassette after the roll of film has been exposed. Some cameras rewind the film automatically.
S. Film cassette – The light –tight container in which 35mm film is packaged.
T. Film Leader - the beginning of the film that is slightly skinnier than the rest. Used to lead the film to be properly loaded.