Objective:- is the lens used closest to the specimen in microscopes or telescopes.
Off the film metering:- is a meter which determines exposure by reading light reflected from the film during exposure. Pioneered by Olympus on its OM2n. Most flash modes have OTF.
Oil reinforcement:- is a method of altering the tonal range of prints on matte or textured fiber papers. The dried print is rubbed with a medium consisting of two parts of turpentine to one of mastic varnish and one of linseed oil. Artists oil color is then applied locally to the print.
One shot color camera:- is an obsolete plate camera making three color separation negatives from a single exposure.
One shot developer:- is a developer that is used on a single occasion and then discarded.
Opacity:- is the light stopping power of a a material. The greater the opacity of a substance, the more light its stops. In photography, opacity is expressed as a ration of the amount of light falling on the surface of the material to the amount of light transmitted by it.
Opalescent:- is like opal, a material with a cloudy-white translucent appearance.
Opal lamp:- is a filament lamp with an opal glass bulb for optimum diffusion.
Opalotype:- is an obsolete printing process in which a carbon-process image is transferred on to translucent opal glass.
Opaque liquid:- is a dense red or black pigment, dissolved in water to form a liquid paint used to fill in film areas that are required to pint as pure white.
Open flash:- is a method of flash operation using the following sequence: shutter opened, flash fired, shutter closed. Usually shutter duration is unimportant since the available light is much dimmer than the flash.
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 bench:- is a device for measuring the optical performance of lenses.
Optical glass:- is used for manufacturing lenses and prisms. It is specially manufactured to be free of defects and distortion, and to withstand heat and humidity. Each type f optical glass is classified according to its refractive index and light dispersive quality. Two or more types of optical glass are typically used in the component elements of photographic lenses.
Optical sensitizing:- is a method of increasing a films sensitivity by the use of dyes.
Optical wedge:- is a strip of material, clear at one end and gradually increasing in opacity, which is used to determine the effect of light intensities on sensitized materials.
Optics:- is the science dealing with the behavior of light.
Ordinary emulsion:- is a term applied to a photographic emulsion which is only sensitive to ultra-violet and blue light.
Orthochromatic:- is used to describe an emulsion which is sensitive to blue and green light, but insensitive to red.
Orth-phenylene diamene:- is a fine-grain developing agent.
Over-development:- is a term indicating that the amount of development recommended by the manufacturer has been exceeded. It can be caused by prolonged development time or an increase in development temperature, and usually results in an increase in density and contrast.
Over-exposure:- is an expression used to indicate that the light sensitive material has been excessively exposed.
Over-run lamp:- is a tungsten light source specifically used at a higher voltage than normal to increase light output and achieve constant color temperature.
Oxalic acid:- are soluble white crystals used in some toners.
Oxidation product:- is the chemical produced by a color developer during the conversion of exposed silver halides to black metallic silver.