Optical telescope

The Large Binocular Telescope uses two curved mirrors to gather light
Schematic of a Keplerian refracting telescope. The arrow at (4) is a (notional) representation of the original image; the arrow at (5) is the inverted image at the focal plane; the arrow at (6) is the virtual image that forms in the viewer's visual sphere. The red rays produce the midpoint of the arrow; two other sets of rays (each black) produce its head and tail.
Eight-inch refracting telescope at Chabot Space and Science Center
The Keck II telescope gathers light by using 36 segmented hexagonal mirrors to create a 10 m (33 ft) aperture primary mirror
These eyes represent a scaled figure of the human eye where 15 px = 1 mm, they have a pupil diameter of 7 mm. Figure A has an exit pupil diameter of 14 mm, which for astronomy purposes results in a 75% loss of light. Figure B has an exit pupil of 6.4 mm, which allows the full 100% of observable light to be perceived by the observer.
Two of the four Unit Telescopes that make up the ESO's VLT, on a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert.
Comparison of nominal sizes of primary mirrors of some notable optical telescopes
Harlan J. Smith Telescope reflecting telescope at McDonald Observatory, Texas

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.

- Optical telescope
The Large Binocular Telescope uses two curved mirrors to gather light

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A biconvex lens

Lens

Transmissive optical device which focuses or disperses a light beam by means of refraction.

Transmissive optical device which focuses or disperses a light beam by means of refraction.

A biconvex lens
Lenses can be used to focus light
Light being refracted by a spherical glass container full of water. Roger Bacon, 13th century
Lens for LSST, a planned sky surveying telescope
Types of lenses
The position of the focus of a spherical lens depends on the radii of curvature of the two facets.
A camera lens forms a real image of a distant object.
Virtual image formation using a positive lens as a magnifying glass.
Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.
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An aspheric biconvex lens.
Close-up view of a flat Fresnel lens.

Other uses are in imaging systems such as monoculars, binoculars, telescopes, microscopes, cameras and projectors.

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Optics

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.

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.

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The Nimrud lens
Alhazen (Ibn al-Haytham), "the father of Optics"
Reproduction of a page of Ibn Sahl's manuscript showing his knowledge of the law of refraction.
The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)
Cover of the first edition of Newton's Opticks (1704)
Geometry of reflection and refraction of light rays
Diagram of specular reflection
Illustration of Snell's Law for the case n1 < n2, such as air/water interface
A ray tracing diagram for a converging lens.
Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.
When oil or fuel is spilled, colourful patterns are formed by thin-film interference.
Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.
Dispersion: two sinusoids propagating at different speeds make a moving interference pattern. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this case, the phase velocity is twice the group velocity. The red dot overtakes two green dots, when moving from the left to the right of the figure. In effect, the individual waves (which travel with the phase velocity) escape from the wave packet (which travels with the group velocity).
Linear polarization diagram
Circular polarization diagram
Elliptical polarization diagram
A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.
The effects of a polarising filter on the sky in a photograph. Left picture is taken without polariser. For the right picture, filter was adjusted to eliminate certain polarizations of the scattered blue light from the sky.
Experiments such as this one with high-power lasers are part of the modern optics research.
VLT's laser guide star
Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina
The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.
Illustrations of various optical instruments from the 1728 Cyclopaedia
Photograph taken with aperture 32
Photograph taken with aperture 5
A colourful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.

Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics.

A 200 mm refracting telescope at the Poznań Observatory

Refracting telescope

A 200 mm refracting telescope at the Poznań Observatory
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Optical diagram of Galilean telescope
y – Distant object; y′ – Real image from objective; y″ – Magnified virtual image from eyepiece;
D – Entrance pupil diameter; d – Virtual exit pupil diameter;  L1 – Objective lens;  L2 – Eyepiece lens e – Virtual exit pupil – Telescope equals
Engraved illustration of a 150 ft focal length Keplerian astronomical refracting telescope built by Johannes Hevelius.
Alvan Clark polishes the big Yerkes achromatic objective lens, over 1 meter across, in 1896.
This 12 inch refractor is mounted in dome and a mount the rotates with the turn of the Earth
The Greenwich 28-inch refractor is a popular tourist attraction in 21st century London
The Apochromatic lens usually comprises three elements that bring light of three different frequencies to a common focus
The 102 cm refractor, at Yerkes Observatory, the largest achromatic refractor ever put into astronomical use (photo taken on 6 May 1921, as Einstein was visiting)
The "Große Refraktor" a double telescope with a 80cm (31.5") and 50 cm (19.5") lenses, was used to discover calcium as an interstellar medium in 1904.
Astronaut trains with camera with large lens
Touristic telescope pointed to Matterhorn in Switzerland
The Yerkes Great refractor mounted at the 1893 World's Fair in Chicago; the tallest, longest, and biggest aperture refactor up to that time.
The 68 cm refractor at the Vienna University Observatory

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

A 150 mm aperture catadioptric Maksutov telescope

Catadioptric system

One where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors (catoptrics).

One where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors (catoptrics).

A 150 mm aperture catadioptric Maksutov telescope
Light path in a Schmidt–Cassegrain
Light path in a meniscus telescope (Maksutov–Cassegrain)
Houghton doublet corrector design equations – special case symmetric design.
Light path in an Argunov Cassegrain telescope
Example of a catadioptric lens using rear surfaced "mangin mirrors" (Minolta RF Rokkor-X 250mm f/5.6)
An example of 'iris blur' or bokeh produced by a catadioptric lens, behind an in-focus light.
500 mm catadioptric lens mounted on a Yashica FX-3
Minolta AF 500 mm F/8 catadioptric lens mounted on a Sony Alpha 55 camera
Samyang 500mm f/8

Catadioptric combinations are used in focusing systems such as searchlights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses.

The 100-inch (2.54 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, USA, used by Edwin Hubble to measure galaxy redshifts and discover the general expansion of the universe.

Telescope

Optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

Optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

The 100-inch (2.54 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, USA, used by Edwin Hubble to measure galaxy redshifts and discover the general expansion of the universe.
17th century telescope
The 60-inch Hale (debuted in 1908) considered to be the first modern large research reflecting telescope.
The primary mirror assembly of James Webb Space Telescope under construction. This is a segmented mirror and its coated with Gold to reflect (orange-red) visible light, through near-infrared to the mid-infrared
Modern telescopes typically use CCDs instead of film for recording images. This is the sensor array in the Kepler spacecraft.
A 1.2-meter (47 in) reflecting telescope
Binoculars
The Very Large Array at Socorro, New Mexico, United States.
Einstein Observatory was a space-based focusing optical X-ray telescope from 1978.
The Compton Gamma Ray Observatory is released into orbit by the Space Shutte in 1991, and it would operate until the year 2000
The reflectors of HEGRA detect flashes of light in the atmosphere, thus detecting high energy particles
Equatorial-mounted Keplerian telescope
A diagram of the electromagnetic spectrum with the Earth's atmospheric transmittance (or opacity) and the types of telescopes used to image parts of the spectrum.
Six views of the Crab nebula supernova remnant, viewed at different wavelengths of light by various telescopes
The Five-hundred-meter Aperture Spherical radio Telescope in Guizhou, China, is the world's largest filled-aperture radio telescope

Optical telescopes, using visible light

Airy diffraction patterns generated by light from two point sources passing through a circular aperture, such as the pupil of the eye. Points far apart (top) or meeting the Rayleigh criterion (middle) can be distinguished. Points closer than the Rayleigh criterion (bottom) are difficult to distinguish.

Angular resolution

Airy diffraction patterns generated by light from two point sources passing through a circular aperture, such as the pupil of the eye. Points far apart (top) or meeting the Rayleigh criterion (middle) can be distinguished. Points closer than the Rayleigh criterion (bottom) are difficult to distinguish.
Log-log plot of aperture diameter vs angular resolution at the diffraction limit for various light wavelengths compared with various astronomical instruments. For example, the blue star shows that the Hubble Space Telescope is almost diffraction-limited in the visible spectrum at 0.1 arcsecs, whereas the red circle shows that the human eye should have a resolving power of 20 arcsecs in theory, though normally only 60 arcsecs.

Angular resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution.

Schematic diagram illustrating how optical wavefronts from a distant star may be perturbed by a layer of turbulent mixing in the atmosphere. The vertical scale of the wavefronts plotted is highly exaggerated.

Astronomical seeing

Astronomical object due to turbulent airflows in the atmosphere of Earth that may become visible as blurring, twinkling or variable distortion.

Astronomical object due to turbulent airflows in the atmosphere of Earth that may become visible as blurring, twinkling or variable distortion.

Schematic diagram illustrating how optical wavefronts from a distant star may be perturbed by a layer of turbulent mixing in the atmosphere. The vertical scale of the wavefronts plotted is highly exaggerated.
Simulated negative image showing what a single (point-like) star would look like through a ground-based telescope with a diameter of 2r0. The blurred look of the image is because of diffraction, which causes the appearance of the star to be an Airy pattern with a central disk surrounded by hints of faint rings. The atmosphere would make the image move around very rapidly, so that in a long-exposure photograph it would appear more blurred.
Simulated negative image showing what a single (point-like) star would look like through a ground-based telescope with a diameter of 7r0, on the same angular scale as the 2r0 image above. The atmosphere makes the image break up into several blobs (speckles). The speckles move around very rapidly, so that in a long-exposure photograph the star would appear as a single blurred blob.
Simulated negative image showing what a single (point-like) star would look like through a ground-based telescope with a diameter of 20r0. The atmosphere makes the image break up into several blobs (speckles). The speckles move around very rapidly, so that in a long-exposure photograph the star would appear as a single blurred blob.
Astronomical observatories are generally situated on mountaintops, as the air at ground level is usually more convective. A light wind bringing stable air from high above the clouds and ocean generally provides the best seeing conditions (telescope shown: NOT).
An animated image of the Moon's surface showing the effects of Earth's atmosphere on the view
Astronomers can make use of an artificial star by shining a powerful laser to correct for the blurring caused by the atmosphere.
This amateur lucky imaging stack using the best of 1800 frames of Jupiter captured using a relatively small telescope approaches the theoretical maximum resolution for the telescope, rather than being limited by seeing.
Slow motion movie of the image seen at a telescope when looking at a star at high magnification (negative images). The telescope used had a diameter of about 7r{{sub|0}} (see definition of r{{sub|0}} below, and example simulated image through a 7r{{sub|0}} telescope). The star breaks up into multiple blobs (speckles) -- entirely an atmospheric effect. Some telescope vibration is also noticeable.

Today, many large scientific ground-based optical telescopes include adaptive optics to overcome seeing.

A collection of different types of eyepieces.

Eyepiece

A collection of different types of eyepieces.
A 25 mm Kellner eyepiece
Simulation of views through a telescope using different eyepieces. The center image uses an eyepiece of the same focal length as the one on the left, but has a wider apparent field of view giving a larger image that shows more area. The image on the right has the same apparent field of view as the center eyepiece but has a shorter focal length, giving the same true field of view as the left image but at higher magnification.
The Plössl, an eyepiece with a large apparent field of view
Examples (from left to right) of 2" (51 mm), 1.25" (32 mm), and 0.965" (24.5 mm) eyepieces.
The eye relief. 1 Real image 2 - Field diaphragm 3 - Eye relief 4 - Exit pupil
Negative lens
Convex lens
Huygens eyepiece diagram
Ramsden eyepiece diagram
Kellner eyepiece diagram
Plössl eyepiece diagram
Orthoscopic eyepiece diagram
Monocentric eyepiece diagram
Erfle eyepiece diagram
König eyepiece diagram
RKE eyepiece diagram
Nagler type 2 eyepiece diagram
Nagler type eyepieces

An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes.

Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I  is the image. Solid blue lines indicate light rays. It can be seen that the image  is formed by actual light rays and thus can form a visible image on a screen placed at the position of the image.

Real image

Image is defined as the collection of focus points of light rays coming from an object.

Image is defined as the collection of focus points of light rays coming from an object.

Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I  is the image. Solid blue lines indicate light rays. It can be seen that the image  is formed by actual light rays and thus can form a visible image on a screen placed at the position of the image.
An inverted real image of distant house, formed by a convex lens, is viewed directly without being projected onto a screen.
Producing a real image. Each region of the detector or retina indicates the light produced by a corresponding region of the object.

This is the mechanism used by telescopes, binoculars and light microscopes.

Diagram of Schmidt camera

Schmidt camera

Diagram of Schmidt camera
The 77 cm Schmidt-telescope from 1966 at Brorfelde Observatory was originally equipped with photographic film, and an engineer is here showing the film-box, which was then placed behind the locker at the center of the telescope (at the telescope's prime focus)
The 2 meter diameter Alfred Jensch Telescope at the Karl Schwarzschild Observatory in Tautenburg, Thuringia, Germany is the largest Schmidt camera in the world.
One of the Baker–Nunn cameras used by the Smithsonian satellite-tracking program
A Baker-Nunn satellite tracking camera in use.

A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations.