A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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.

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) Colouring used in photography to render parts of a negative opaque.

OPEN UP - Increase aperture size or reduce shutter speed to permit more light to reach the film.

OPTICAL GLASS - High-quality, color-free glass having specific refractive qualities, used in lenses and other components of optical systems.

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 colours as found in a photographic subject. (2) A photographic emulsion sensitive to all visible colours except red - i.e. an ortho film is sensitive to blue and green light.

OTF - Off the film

OVER-EXPOSE - Expose a photographic emulsion to more than light than is necessary for proper exposure.

OVEREXPOSURE - Overexposure occurs when a photograph receives too much light. It results in a loss of resolution (very fine detail), more graininess and less detail in highlight areas. An overexposed negative is very dense resulting in light prints. A slide has very light density. Intentional over-exposure or underexposure is known as increasing or decreasing exposure.