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IF - Abbreviation for “Internal Focusing”
IMAGE - A term commonly substituted for "photograph" or "picture," an image is a two-dimensional reproduction of a scene.
IMAGE SENSOR - Also called the "imaging sensor" or just the "sensor." A digital camera's image sensor records the scene being photographed in a similar manner to film in a traditional camera. Unlike film, the image sensor does not store the image. It is stored on the digital camera's media.
IMAGE STABILIZATION - often referred to as “IS” and also known as “Vibration reduction” or “VR” - A feature in some lenses and camera bodies that minimizes the effect of camera shake at slow shutter speeds, helping to prevent image blur. Optical IS, the preferred method, employs sensors that detect camera motion and compensate for its effects by moving lens elements or by moving the camera’s image sensor, and Digital IS employs software. You may come across the term “Anti-shake,” which is not image stabilization technology, but instead increases a camera’s ISO sensitivity to provide a faster shutter speed.
INCIDENT LIGHT - Light falling on a surface - not the light reflected from it. Incident light rays are those that strike an object.
An INCIDENT LIGHT METER reads the light falling on the subject.
INCIDENT LIGHT METER - An exposure meter (generally hand held as opposed to a reflective meter that is built into a camera) that reads the amount of incident light. Since the meter does not read the light reflected from the subject, the subject's reflectance does not affect the exposure reading. Incident light meters are equipped with one of two types of light receptor diffusion cover - a round diffuser for three-dimensional subjects and a flat one for two-dimensional, flat subjects, such as a map or painting. Also called an “Ambient light meter.”
INDEX PRINT - Thumbnail-size prints on a single sheet showing all photographs taken on a roll of film. Each tiny print is individually identified for printing.
INFINITY - Distance from the camera that is far enough away that any object at or beyond it will be reproduced sharply when the lens is focused on its infinity setting. The infinity setting is usually identified by the ∞ symbol.
INFRARED FILM - Photographic film that is sensitive to infrared radiation.
INFRARED FOCUSING INDICATOR - A mark on the barrel of a lens that indicates proper focusing when using infrared film. The mark is typically a red or white line that is slightly apart from the focusing indicator for normal film. Sometimes the letter "R" is next to it.
INITIALIZING - Also known as formatting, initializing refers to the preparation of a digital camera's image memory card's contents to enable digital image data recording.
INTENTIONAL OVER- or UNDER-EXPOSURE - Intentional over-exposure or underexposure is known as increasing or decreasing exposure. Many professional photographers will consistently underexpose (decrease exposure of) some slide films on purpose.
INTERCHANGEABLE LENS - One of a system of detachable lenses of different characteristics, generally focal length variety, each of which fits a given camera body.
INTERNAL FOCUSING - Lens in which internal lens groups shift during focusing so that the external length of the lens does not change.
INTERPOLATION - Adding new pixels to a digital image between existing pixels. Interpolation software analyzes the adjacent pixels to create the new ones when enlarging an image file.
INTERVALOMETER - A camera’s device that takes a number of consecutive exposures at set intervals for time-lapse photography. Some cameras have built-in intervalometers; others can be fitted with an accessory intervalometer.
INVERSE SQUARE LAW - An equation that relates the intensity of a light source to the illumination it produces at a given distance. Light diminishes over distance in accordance with the Inverse square law, which states that doubling the flash-to-subject distance reduces the light falling on the subject to one-quarter.
The IRIS DIAPHRAGM controls the size of the aperture (the lens opening).
IQ - Traditionally understood as Intelligence Quotient, a test score intended to measure human intelligence. When referring to cameras, IQ has come to mean Image Quality - a picture quality level that is not specifically defined.
IRIS DIAPHRAGM - Also sometimes simply known as “iris,” a device inside a lens of thin overlapping metal leaves that move inwards or outwards, creating an aperture of variable size. The aperture size controls the amount of light passing through the lens to the sensor or film.
ISO - Film speed or digital photography sensitivity is designated by a single, almost universally-accepted common rating system developed by the International Organization for Standardization which uses the initials “ISO” before the film-speed number or digital camera's sensitivity setting number - e.g. ISO 100. (Note that many sources will tell you that the initials I.S.O. stand for "International Standards Organization," but they do not.)
IX - A feature of the APS (Advanced Photo System) is its encoding on the film itself of picture-taking and processing data. IX (Information Exchange) technology allows photofinishing equipment to read instructions on the film and therefore make processing and printing adjustments to provide the best results from different lighting and exposure conditions, and also allows such features as mid-roll change.