optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

and

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employe ...

, infinity focus is the state where a

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

or other optical system forms an image of an object an

infinite Infinite may refer to: Mathematics * Infinite set, a set that is not a finite set *Infinity, an abstract concept describing something without any limit Music *Infinite (group), a South Korean boy band *''Infinite'' (EP), debut EP of American m ...

distance away. This corresponds to the point of focus for parallel

rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...

. The image is formed at the focal point of the lens. In simple two lens systems such as a

refractor telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...

, the object at infinity forms an image at the focal point of the

objective lens In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a single lens or mirror, or combinations of several optical elem ...

, which is subsequently magnified by the eyepiece. The magnification is equal to the focal length of the objective lens divided by the focal length of the eyepiece. In practice, not all

photographic lens A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capab ...

es are capable of achieving infinity focus by design. A lens used with an adapter for close-up focusing, for example, may not be able to focus to infinity. Failure of the human eye to achieve infinity focus is diagnosed as myopia. All optics are subject to manufacturing tolerances; even with perfect manufacture, optical trains experience

thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic ...

. Focus mechanisms must accommodate part variations; even custom-built systems may have some means of adjustment. For example, telescopes such as the

Mars Orbiter Camera The Mars Orbiter Camera and Mars Observer Camera (MOC) were scientific instruments on board the Mars Observer and Mars Global Surveyor spacecraft. The camera was built by Malin Space Science Systems (MSSS) for NASA and the cost of the whole MOC s ...

, which are nominally set to infinity, have thermal controls. Deviations from its operating temperature are actively compensated to prevent shifts of focus.

References

Geometrical optics Science of photography {{Optics-stub

See also

References