Police Photography Flashcards
Purpose of crime/accident scene photography
- to provide a permanent visual record
- to show particular items of evidence and their relationship to the scene
- to make close up records of significant portions of the scene
- to refresh memory, substantiate testimony and clarify understanding
Three criteria of photography as evidence
Accurate-“a fair and accurate representation of the scene as it appeared”
Authentic-not staged or recreated unless specifically indicated as being so, otherwise the scene is to be photographed as found
Relevant-the photo must pertain to an issue before the court, like any other evidence
The portion of a scene that is seen through the camera lens. Angle of view is determined by the focal length of the lens used. Wide angle sees more, telephoto lens sees less. A “normal” lens views similar to human eye.
Angle of view
The variable sized opening in the lens, used to control the amount of light allowed to pass on to the film. The lens opening is usually expressed in f-numbers.
Aperture
A numerical rating of a film’s light sensitivity. Lower rated films are less sensitive to light and require more light for proper exposure. Lower rated films provide more detail. Allows greater enlargement without graininess
ASA/ISO
Shooting a number of photos of the same subject, from the same viewpoint, at different levels of exposure to ensure at least one properly exposed print. Usually done by intentionally under exposing and overexposing around what is believed to be an optimal exposure.
Bracketing
The range of sharp focus in a photograph. The distance between the nearest and farthest parts of the subject or scene that will appear acceptably sharp on the film.
Depth of field
The distance, measured in millimeters, from the optical center of the lens to the film plane where objects at infinity are brought into sharp focus.
Focal length
The shutter system of most SLRS. A pair of moving curtains or blades that opens to form a slit that moves directly in front of the film to allow an image to form.
Focal plane shutter
The point at which light converges to form a sharp image. Achieved by adjusting the distance scale of the lens so that a selected part of the subject appears sharp.
Focus
Numbers used to indicate the size of the lens opening that allows light to enter the camera and expose the film. The smaller the number the larger the opening and vice versa
F-Stops
How to calculate f-stop
Dividing the focal length of the lens by the diameter of the lens opening. Best thought of as a fraction. F-2 is half the size of the lens’ focal length: 50mm lens on f-2, the aperture is 25mm wide.
The measure of power of a flash unit.
Guide number.
With a small light source, like a flash unit, it’s intensity is inversely proportional to the square of the distance from the light source: twice the distance, one quarter the light intensity.
Inverse square law
The three factors influencing proper exposure are: film speed, aperture, shutter speed, the distance from flash to subjects becomes a fourth factor, if flash, rather than ambient light is used.
Exposure triangle
One stop change of shutter speed or f-stop setting represents a halving or doubling of the light allowed to reach the film. Each doubling of exposure must be accompanied with a halving of exposure by the other setting.
Reciprocal exposure
The number indicating the amount of time that light is allowed to reach the film in the camera. Designations are in fractions of a second: 30 is actually 1/30th of a second.
Shutter speed
A camera in which the scene to be photographed is reflected by a mirror, onto a glass where it can be focused n composed. The scene is viewed through the same lens that takes the picture. When the picture is taken, the mirror swings out of the way allowing light to strike the film.
SLR: single lens reflex
The shutter speed of a particular camera that ensures the entire film area is exposed when the flash unit fires.
Sync speed
An inherent quality of lenses is that the area of sharpness for any subject extends one third in front of and two thirds behind the prime subject.
Zone focusing
Selective focus-Width
The eye focuses on one object at a time. To eliminate distracting elements from the scene you must:
Come in closer to the subject, cutting out detail to the sides of primary subject
Use a longer focal length lens with a narrower angle of view
Use a zoom lens, which can also narrow the angle of view
Selective Focus- Depth
The eye focuses on one object at a time. The camera can be set so that near, far and mid-distance objected are simultaneously in focus. By manipulating exposure settings, the photographer chooses how deep the area rendered in focus will be.
Motion
The camera can create a blur using a relatively long shutter speed. The camera can capture an object as perceived by the eye. The camera can capture minute parts of a sequence occurring too fast for the eye to perceive.
The normal lens
For 35mm SLR cameras, this is usually a 50 mm lens. Provides photo image close to how the eye originally perceived the scene. No distortion a between far and near objects.
