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The pupil magnification of an optical system is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. The pupil magnification is used in calculations of the effective f-number, which affects a number of important elements related to optics, such as exposure, diffraction, and depth of field. For all symmetric lenses, and for many conventional photographic lenses, the pupils appear the same size and so the pupil magnification is approximately 1.
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In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with the nature of the distortion depending on the type of aberration. Aberration can be defined as a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements.
In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. By incorporating index of refraction in its definition, NA has the property that it is constant for a beam as it goes from one material to another, provided there is no refractive power at the interface. The exact definition of the term varies slightly between different areas of optics. Numerical aperture is commonly used in microscopy to describe the acceptance cone of an objective, and in fiber optics, in which it describes the range of angles within which light that is incident on the fiber will be transmitted along it.
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models.
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil. It is also known as the focal ratio, f-ratio, or f-stop, and is very important in photography. It is a dimensionless number that is a quantitative measure of lens speed; increasing the f-number is referred to as stopping down. The f-number is commonly indicated using a lower-case hooked f with the format f/N, where N is the f-number.
In optics, a circle of confusion (CoC) is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. It is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot.
The angle of view is the decisive variable for the visual perception of the size or projection of the size of an object.
A spotting scope is a compact high-power telescope optimized for detailed observation of distant objects. They are used as portable optical enhancement devices for various outdoor activities such as birdwatching, skygazing and other naturalist activities, for hunting and target shooting to verify a marksman's shot placements, for tactical ranging and surveillance, and for any other application that requires higher magnification than ordinary binoculars.
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocular are typically less than half of a pair of binoculars with similar optical properties, making it more portable and also less expensive. This is because binoculars are essentially a pair of monoculars packed together — one for each eye. As a result, monoculars only produce two-dimensional images, while binoculars can use two parallaxed images to produce binocular vision, which allows stereopsis and depth perception.
An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors.
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 elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.
Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in size, sometimes called minification or de-magnification.
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.
Macro photography is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size . By the original definition, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater. In some senses, however, it refers to a finished photograph of a subject that is greater than life size.
A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a reticle – mounted in a focally appropriate position in its optical system to provide an accurate point of aim. Telescopic sights are used with all types of systems that require magnification in addition to reliable visual aiming, as opposed to non-magnifying iron sights, reflector (reflex) sights, holographic sights or laser sights, and are most commonly found on long-barrel firearms, particularly rifles, usually via a scope mount. The optical components may be combined with optoelectronics to add night vision or smart device features.
In optics, the exit pupil is a virtual aperture in an optical system. Only rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a telescope or compound microscope, this image is the image of the objective element(s) as produced by the eyepiece. The size and shape of this disc is crucial to the instrument's performance, because the observer's eye can see light only if it passes through this tiny aperture. The term exit pupil is also sometimes used to refer to the diameter of the virtual aperture. Older literature on optics sometimes refers to the exit pupil as the Ramsden disc, named after English instrument-maker Jesse Ramsden.
The eye relief of an optical instrument is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye is outside this distance, a reduced field of view will be obtained. The calculation of eye relief is complex, though generally, the higher the magnification and the larger the intended field of view, the shorter the eye relief.
In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the front of the lens system. The corresponding image of the aperture as seen through the back of the lens system is called the exit pupil. If there is no lens in front of the aperture, the entrance pupil's location and size are identical to those of the aperture. Optical elements in front of the aperture will produce a magnified or diminished image that is displaced from the location of the physical aperture. The entrance pupil is usually a virtual image: it lies behind the first optical surface of the system.
A telecentric lens is a special optical lens that has its entrance or exit pupil, or both, at infinity. Telecentric lenses are often used for precision optical two-dimensional measurements or reproduction and other applications that are sensitive to the image magnification or the angle of incidence of light.
The study of image formation encompasses the radiometric and geometric processes by which 2D images of 3D objects are formed. In the case of digital images, the image formation process also includes analog to digital conversion and sampling.