Photographic Glossary-O


OCR (Optical Character Recognition)
A technology that allows dots or pixels within characters inside a bitmapped image to be converted into an ASCII text file. This text file can be edited.

Off-The-Film Metering
A meter which determines exposure by reading light reflected from the film during picture-taking or a way of metering meters light reflects off film plane during exposure. First pioneered by Olympus on its famous OM2n, which is real time metering for normal exposure and flash exposures. Most flash mode for modern cameras are with OTF flash mode now.

Online Service
A commercial service that gives computer users Internet access and connection to a variety of online offerings, such as shopping, games and chat rooms.

The degree to which an object blocks light. Technically, opacity is expressed as a ratio of the incident light to the transmitted light.

Opening up
Is increasing the size of the lens aperture or decreasing the shutter speed to admit more light to the film.

Optical axis
Is an imaginary line passing horizontally through the center of a compound lens system.

Optical disk
A digital storage system commonly used for mass storage.

Optical filtering
Selectively transmitting or blocking a range of wavelengths of light.

Optical frequency response
A scanner's capability for capturing a given frequency or range of frequencies.

Optical resolution
The true resolution of a scanner and the key factor in determining the amount of detail visible in a image. Optical resolution is one type of resolution; the other is interpolated resolution.

Optical Scanner
A device that changes images from either reflection or transparency medium to digital data.

Optical storage
A peripheral device for storing data. It may be WORM or rewritable.

Optical viewfinder
A viewfinder system that shows a similar view to that seen by the camera lens ( as on 35mm compact cameras ) Useful because it uses no power, but can cause parallax and focus errors.

Optical Zoom
An optical zoom is made to bring you closer to your subject, without you having to move. Zooms are constructed to allow a continuously variable focal length, without disturbing focus. To achieve this, the optical zoom uses a combination of lenses that magnify the image prior to being registered at high resolution by the sensor. While the digital zoom only changes the presentation of existing data, the optical zoom actually augments the data collected by the sensor. Optical zooms are superior to digital zooms.

An image printed on glass then backed in gold; also called gold-tone or curt-tone. It is often found in ornate, molded or gilded frames.

Ortho (Orthochromatic)
Denotes film sensitive to blue and green light.

Orthochromatic ( Ortho film )
Black-and-white emulsions that are not equally sensitive to all colours of light. They are more sensitive to blue and green, but not sensitive to red light. Films that can be handled under a red safelight. Used primarily in print shops. Example: Kodalith

OTF Test (Optical Transfer Functions)
Evaluates lens performance in terms of resolving power, contrast rendition and aberrations. Most believes the test is the only way to determine how good a lens is in the lab - at least the tester (esp photo magazines) does.

Refers to an image created when the rays of light passing through a lens fall upon a plane in front of or beyond the point at which they converge to form a sharp image. Out-of-focus images appear blurred or fuzzy.

Output resolution
The detail and clarity (achieved by tightness of dots) with which the image will be displayed or printed (dependent on the capability of the display or printing device).

To give more than normal the amount of development.

A condition in which too much light reaches the film, producing a dense negative or a very bright/light print or slide. To give more than normal exposure to film or paper. The resulting silver is often too great for best results.

Scanning at more than an optimum sampling rate.

Loss of chemical activity due to contact with oxygen in the air.