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OBJECTIVE - An objective (or object lens, object glass, objective lens or photographic objective) is an optical system or device containing a combination of lenses that receive light rays from an object and form an image on the focal plane. A photographic lens is an objective.
OCCLUDE - To block the passage of, as in "to occlude light."
OFF THE FILM METERING - Known also by its initials, OTF metering is an exposure meter reading that measures light reflected from the surface of the film during exposure.
OPACITY - (1) State or quality of being opaque. (2) The degree to which a substance is or may be opaque. (3) The proportion of the light that is absorbed by the emulsion on any given area of the negative.
OPAQUE - (1) Does not transmit light. (2) Coloring used in photography to render parts of a negative opaque.
OPAQUE BODIES - Objects that permit no light to pass through them, but reflect light.
OPEN UP - Increase aperture size to permit more light to reach the film or image sensor. If you change your lens's aperture from ƒ/11 to ƒ/8, a larger opening, you have opened up by one stop.
OPTICAL GLASS - High-quality, color-free glass having specific refractive qualities, used in lenses and other components of optical systems.
OPTICAL RESOLUTION - Also referred to as "True resolution," it means an image's non-interpolated pixel dimensions.
Some cameras like this dSRL have optical and electronic viewfinders.
OPTICAL VIEWFINDER - A camera's viewfinder (including those of dSLR cameras) that does not involve an LCD screen or an electronic aid to view a scene. Think of a telescope or binoculars that are purely optical and have no electronic components.
OPTICAL ZOOM - A true zoom effect unlike a digital camera's digital zoom. Optical zoom changes the focal length of a lens.
OPTICS - The branch of physical science that deals with the properties and phenomena of both visible and invisible light and with vision.
ORTHOCHROMATIC or "Ortho" - (1) Representing correctly the relations of colors as found in a photographic subject. (2) A photographic emulsion sensitive to all visible colors except red - i.e. an ortho film is sensitive to blue and green light.
OTF - Off the film. (Some cameras' built-in exposure meters take their readings from light reflected off the film.)
OVER-EXPOSE - Expose a photographic emulsion or a digital image sensor to more than light than is necessary for proper exposure.
OVEREXPOSURE - Overexposure occurs when a sensor or film receives too much light causing the resulting photograph to be improperly exposed by too much light. It results in a loss of resolution (very fine detail), more graininess or digital noise and less detail in highlight areas. An overexposed negative is very dense resulting in light prints. An overexposed slide, or over-exposure with a digital camera, displays very light density. Intentional over-exposure or underexposure is known as increasing or decreasing exposure. An overexposed image is sometimes referred to as a "bleached out" photograph.
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