Astrophotography
Encyclopedia
Astrophotography is a specialized type of photography
that entails recording images of astronomical object
s and large areas of the night sky. The first photographs of an astronomical object (the moon) were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon
, Sun
, and planet
s, astrophotography has the ability to image objects invisible to the human eye such as dim star
s, nebula
e, and galaxies
. This is done by long time exposure since both film and digital cameras can accumulate and sum light photon
s over these long periods of time. In professional astronomical research photography revolutionized the field, with long time exposures recording hundreds of thousands of new stars and nebulae that were invisible to the human eye, leading to specialized and ever larger optical telescopes that were essentially big "cameras" designed to collect light to be recorded on film. Direct astrophotography had an early role in sky surveys and star classification but over time it has given way to more sophisticated equipment and techniques designed for specific fields of scientific research, with film (and later astronomical CCD cameras) becoming just one of many forms of sensor
.
Astrophotography is a large sub-discipline in amateur astronomy
where it is usually used to record aesthetically pleasing images, rather than for scientific research, with a whole range of equipment and techniques dedicated to the activity.
With only a few exceptions, astronomical photography employs long exposures
since both film and digital imaging devices can accumulate and sum light photon
s over long periods of time. The amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics (the objective
) being used. Urban areas produce light pollution
so equipment and observatories doing astronomical imaging are located in remote locations to allow long exposures without the film or detectors being swamped with stray light.
Since the Earth is constantly rotating, telescopes and equipment have to be rotated in the opposite direction to follow the apparent motion of the stars overhead (called diurnal motion
). This is accomplished by using either equatorial
or computer controlled altazimuth
telescope mounts to keep celestial objects centered while the earth rotates. All telescope mount
systems suffer from induced tracking error due to imperfect motor drives and mechanical sag of the telescope. Tracking errors are corrected by keeping a selected aiming point, usually a bright guide star
, centered during the entire exposure. Sometimes (as in the case of comet
s) the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. This guiding is done through a second co-mounted telescope called a "guide scope" or via some type of "off-axis guider", a device with a prism or optical beam splitter
that allows the observer to view the same image in the telescope that is taking the picture. Guiding was formerly done manually throughout the exposure with an observer standing at (or riding inside) the telescope making corrections to keep a cross hair on the guide star. Since the advent of computer controlled systems this is accomplished by an automated systems in professional and even amateur equipment.
Astronomical photography is one of the earliest types of scientific photography and almost from its inception it diversified into subdisciplines that each have a specific goal including star cartography
, astrometry
, stellar classification
, photometry
, spectroscopy
, polarimetry
, and the discovery of astronomical objects such as asteroids, meteor
s, comet
s, variable star
s, nova
e, and even unknown planet
s. These all require specialized equipment such as telescopes designed for precise imaging, for wide field of view (such as Schmidt camera
s), or for work at specific wavelengths of light. Astronomical CCD cameras may use cryogenic
cooling to reduce thermal noise and to allow the detector to record images in other spectra such as in infrared astronomy
. Specialized filters
are also used to record images in specific wavelengths.
The development of astrophotography as a scientific tool was pioneered in the mid-19th century for the most part by experimenters and amateur astronomers, or so-called "gentleman scientist
s" (although, as in other scientific fields, these were not always men). Because of the very long exposures needed to capture relatively faint astronomical objects, many technological problems had to be overcome. These included making telescopes rigid enough so they wouldn’t sag out of focus during the exposure, building clock drives that could rotate the telescope mount at a constant rate, and developing ways to accurately keep a telescope aimed at a fixed point over a long period of time. Early photographic processes also had limitations. The daguerreotype
process was far too slow to record anything but the brightest objects, and the wet plate collodion
process limited exposures to the time the plate could stay wet. The first known attempt at astronomical photography was by Louis Jacques Mandé Daguerre, inventor of the daguerreotype process which bears his name, who attempted in 1839 to photograph the moon
. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot. John William Draper
, an American physician, chemist and scientific experimenter, managed to make the first successful photograph of the moon a year later on March 23, 1840, taking a 20-minute-long daguerreotype
image using a 5-inch (13 cm) reflecting telescope
. The first photograph of a star was a daguerreotype of the star Vega
by astronomer William Cranch Bond
and daguerreotype photographer and experimenter John Adams Whipple
, on July 16 and 17, 1850 with Harvard College Observatory
's 15 inch Great refractor
.
In 1863 the English chemist William Allen Miller
and English amateur astronomer Sir William Huggins
used the wet collodion plate process to obtain the first ever photographic spectrogram
of a star, Sirius
and Capella
. In 1872 American physician Henry Draper
, the son of John William Draper, recorded the first spectrogram of a star (Vega) to show absorption lines.
Astronomical photography did not become a serious research tool until the late 19th century, with the introduction of dry plate
photography. It was first used by Sir William Huggins and his wife Margaret Lindsay Huggins
, in 1876, in their work to record the spectra of astronomical objects. In 1880 Henry Draper used the new dry plate process with an 11-inch (28 cm) refracting telescope
to make a 51-minute exposure of the Orion Nebula
, the first photograph of a nebula ever made. A breakthrough in astronomical photography came in 1883, when amateur astronomer Andrew Ainslie Common
used the dry plate process to record several images of the same nebula in exposures up to 60 minutes with a 36-inch (91 cm) reflecting telescope that he constructed in the backyard of his home in Ealing, outside London. These images for the first time showed stars too faint to be seen by the human eye.
1887 saw the Astrographic Catalogue and Carte du Ciel
, the first all-sky photographic astrometry
project. It was conducted by 20 observatories all using special photographic telescopes with a uniform design called normal astrograph
s, all with an aperture of around 13 inches (330 mm) and a focal length of 11 feet (3.4 m), designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm while covering a 2° × 2° field of view. The attempt was to accurately map the sky down to the 14th magnitude
but it was never completed.
The beginning of the 20th century saw the worldwide construction of refracting telescopes and sophisticated large reflecting telescopes specifically designed for photographic imaging. Towards the middle of the century, giant telescopes such as the 200-inch (5 meter) Hale Telescope
and the 48-inch Samuel Oschin telescope
at Palomar Observatory
were pushing the limits of film photography.
Some progress was made in the field of photographic emulsions and in the techniques of forming gas hypersensitization
, cryogenic cooling, and light amplification, but starting in the 1970s after the invention of the CCD, photographic plates have given way to electronic imaging in professional observatories. CCD's are far more light sensitive, do not drop off in sensitivity to light over long exposures the way film does ("reciprocity failure"), have the ability to record in a much wider spectral range, and simplify storage of information. Telescopes now use many configurations of CCD sensors including linear arrays and large mosaics of CCD elements equivalent to 100 million pixels, designed to cover the focal plane of telescopes that formerly used 10-to-14-inch photographic plates.
The late 20th century saw advances in astronomical imaging take place in the form of new hardware, with the construction of giant multi-mirror and segmented mirror
telescopes. It would also see the introduction of space based telescopes, such as the Hubble Space Telescope
. Operating outside the atmosphere’s turbulence, scattered ambient light and the vagaries of weather allows the Hubble Space Telescope, with a mirror diameter of 2.4 m, to record stars down to the 30th magnitude, some 100 times dimmer than what the 5-meter Mount Palomar Hale telescope could record in 1949.
s, 35 mm film
, digital single-lens reflex camera
s, simple amateur-level and professional-level commercially manufactured astronomical CCD cameras, video camera
s, and even off-the-shelf webcam
s adapted for long-exposure imaging.
Conventional over-the-counter film has long been used for astrophotography. Film exposures range from 10 minutes to over an hour. Commercially available color film stock is subject to reciprocal failure
over long exposures, in which sensitivity to light of different wavelengths appears to drop off as the exposure time increases, leading to color shift in the image. This is compensated for by using the same technique used in professional astronomy of taking photographs at different wavelengths that are then combined to create a correct color image. Since film is much slower than digital sensors, tiny errors in tracking can be corrected without much noticeable effect on the final image. Film astrophotography is becoming less popular due to the general spread of low-cost digital cameras and a diminishing supply of suitable film emulsions. Also, film requires continuous on-going costs (film, processing, printing or scanning).
Since the late 1990s amateurs have been following the professional observatories in the switch from film to digital CCDs for astronomical imaging. CCDs are more sensitive than film, allowing much shorter exposure times, and have a linear response to light. Images can be captured in many short exposures to create a synthetic long exposure. Digital cameras also have minimal or no moving parts and the ability to be operated remotely via an infrared remote or computer tethering, limiting vibration. Simple digital devices such as webcam
s can be modified to allow access to the focal plane and even (after the cutting of a few wires), for long exposure
photography. Digital video cameras are also used. There are many techniques and pieces of commercially manufactured equipment for attaching digital single-lens reflex cameras and even basic point and shoot cameras to telescopes. Consumer level digital cameras suffer from image noise
over long exposures, so there are many techniques for cooling the camera, including cryogenic
cooling. Astronomical equipment companies also now offer a wide range of purpose-built astronomical CCD cameras complete with hardware and processing software.
software to improve the image in some way. Images can be brightened and manipulated in a computer to adjust color and increase the contrast. More sophisticated techniques involve capturing multiple images (sometimes thousands) to composit together in an additive process to sharpen images to overcome poor atmospheric seeing, negating tracking issues, bringing out faint objects with a poor signal-to-noise ratio
, and filtering out light pollution. Digital camera images may also need further processing to reduce the image noise
from long exposures, including subtracting a “dark frame”
and a processing called image stacking or "Shift-and-add
". There are several commercial and freeware
software packages available specifically for astronomical photographic image manipulation.
. Urban astrophotographers use special light-pollution filters and advanced computer processing techniques to remove ambient urban light from the background of their images. They may also stick to imaging bright targets like the moon and planets. Another method used by amateur astronomers to avoid light pollution is to set up, or rent time, on a remotely operated telescope at a dark sky location. Other challenges include setup and alignment of portable telescopes for accurate tracking, working within the limitations in “off the shelf” equipment, the endurance of monitoring equipment, and sometimes manually tracking astronomical objects over long exposures in a wide range of weather conditions.
The most basic types of astronomical photographs are made with standard cameras and photographic lenses mounted in a fixed position or on a tripod. Foreground objects or landscapes are sometimes composed in the shot. Objects imaged are constellation
s, interesting planetary configurations, meteors, and bright comets. Exposure times must be short (under a minute) to avoid having the stars point image become an elongated line due to the Earth's rotation. Camera lens focal lengths are usually short, as longer lenses will show image trailing in a matter of seconds. Allowing the stars to intentionally become elongated lines in exposures lasting several minutes or even hours, called “Star trails”, is an artistic technique sometimes used.
Tracking mounts
To achieve longer exposures without objects being blurred, some form of tracking mount is usually employed to compensate for the Earth's rotation, including commercial equatorial mounts and homemade equatorial devices such as barn door tracker
s and equatorial platform
s.
"Piggyback" photography
Piggyback astronomical photography is a method where a camera/lens is mounted on an equatorially mounted astronomical telescope. The telescope is used as a guide scope to keep the field of view centered during the exposure. This allows the camera to use a longer exposure and/or a longer focal length lens or even be attached to some form of photographic telescope co-axial with the main telescope.
Telescope focal plane photography
In this type of photography the telescope itself is used as the "lens" collecting light for the film or CCD of the camera. Although this allows for the magnification and light gathering power of the telescope to be used, it is one of the most difficult astrophotography methods. This is because of the difficulties in centering and focusing sometimes very dim objects in the narrow field of view, contending with magnified vibration and tacking errors, and the added expense of equipment (such as sufficiently sturdy telescope mounts, camera mounts, camera couplers, off axis guiders, guide scopes, illuminated cross-hairs, or auto-guiders mounted on primary telescope or the guide-scope.) There are several different ways cameras (with removable lenses) are attached to amateur astronomical telescopes including:
When the camera lens is not removed (or cannot be removed) a common method used is afocal photography
, also called afocal projection. In this method both the camera lens and the telescope eyepiece are attached. When both are focused at infinity the light path between them is parallel (afocal
), allowing the camera to basically photograph anything the observer can see. This method works well for capturing images of the moon and brighter planets, as well as narrow field images of stars and nebulae. Afocal photography was common with early 20th century consumer level cameras, since many models had non-removable lenses. It has grown in popularity with the introduction of point and shoot digital cameras since most models also have non-removable lenses.
Imaging can done regardless of the location of the user or the telescopes they wish to use. The digital data collected by the telescope is then transmitted and displayed to the user by means of the Internet. An example of a digital remote telescope operation for public use via the Internet is The Bareket Observatory
.
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
that entails recording images of astronomical object
Astronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...
s and large areas of the night sky. The first photographs of an astronomical object (the moon) were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
, Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, and planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s, astrophotography has the ability to image objects invisible to the human eye such as dim star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s, nebula
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
e, and galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
. This is done by long time exposure since both film and digital cameras can accumulate and sum light photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s over these long periods of time. In professional astronomical research photography revolutionized the field, with long time exposures recording hundreds of thousands of new stars and nebulae that were invisible to the human eye, leading to specialized and ever larger optical telescopes that were essentially big "cameras" designed to collect light to be recorded on film. Direct astrophotography had an early role in sky surveys and star classification but over time it has given way to more sophisticated equipment and techniques designed for specific fields of scientific research, with film (and later astronomical CCD cameras) becoming just one of many forms of sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
.
Astrophotography is a large sub-discipline in amateur astronomy
Amateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
where it is usually used to record aesthetically pleasing images, rather than for scientific research, with a whole range of equipment and techniques dedicated to the activity.
Overview
Exposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
since both film and digital imaging devices can accumulate and sum light photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s over long periods of time. The amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics (the objective
Objective (optics)
In an optical instrument, 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 single lenses or mirrors, or combinations of several optical elements. They are used in microscopes, telescopes,...
) being used. Urban areas produce light pollution
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
so equipment and observatories doing astronomical imaging are located in remote locations to allow long exposures without the film or detectors being swamped with stray light.
Since the Earth is constantly rotating, telescopes and equipment have to be rotated in the opposite direction to follow the apparent motion of the stars overhead (called diurnal motion
Diurnal motion
Diurnal motion is an astronomical term referring to the apparent daily motion of stars around the Earth, or more precisely around the two celestial poles. It is caused by the Earth's rotation on its axis, so every star apparently moves on a circle, that is called the diurnal circle. The time for...
). This is accomplished by using either equatorial
Equatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
or computer controlled altazimuth
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
telescope mounts to keep celestial objects centered while the earth rotates. All telescope mount
Telescope mount
A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument...
systems suffer from induced tracking error due to imperfect motor drives and mechanical sag of the telescope. Tracking errors are corrected by keeping a selected aiming point, usually a bright guide star
Guide star
In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a heavenly body, whose motion across the sky is primarily due to the rotation of the Earth....
, centered during the entire exposure. Sometimes (as in the case of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s) the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. This guiding is done through a second co-mounted telescope called a "guide scope" or via some type of "off-axis guider", a device with a prism or optical beam splitter
Beam splitter
A beam splitter is an optical device that splits a beam of light in two. It is the crucial part of most interferometers.In its most common form, a rectangle, it is made from two triangular glass prisms which are glued together at their base using Canada balsam...
that allows the observer to view the same image in the telescope that is taking the picture. Guiding was formerly done manually throughout the exposure with an observer standing at (or riding inside) the telescope making corrections to keep a cross hair on the guide star. Since the advent of computer controlled systems this is accomplished by an automated systems in professional and even amateur equipment.
Astronomical photography is one of the earliest types of scientific photography and almost from its inception it diversified into subdisciplines that each have a specific goal including star cartography
Star cartography
Celestial cartography, uranography or star cartography, is the fringe of astronomy and branch of cartography concerned with mapping stars, galaxies, and other astronomical objects on the celestial sphere...
, astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
, stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, photometry
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...
, spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
, polarimetry
Polarimetry
Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves...
, and the discovery of astronomical objects such as asteroids, meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
s, comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s, variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s, nova
Nova
A nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
e, and even unknown planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s. These all require specialized equipment such as telescopes designed for precise imaging, for wide field of view (such as Schmidt camera
Schmidt camera
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. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
s), or for work at specific wavelengths of light. Astronomical CCD cameras may use cryogenic
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...
cooling to reduce thermal noise and to allow the detector to record images in other spectra such as in infrared astronomy
Infrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
. Specialized filters
Filter (optics)
Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....
are also used to record images in specific wavelengths.
History
Gentleman scientist
A gentleman scientist is a financially independent scientist who pursues scientific study as a hobby. The term arose in post-Renaissance Europe but became less common in the 20th century as government and private funding increased.-History:...
s" (although, as in other scientific fields, these were not always men). Because of the very long exposures needed to capture relatively faint astronomical objects, many technological problems had to be overcome. These included making telescopes rigid enough so they wouldn’t sag out of focus during the exposure, building clock drives that could rotate the telescope mount at a constant rate, and developing ways to accurately keep a telescope aimed at a fixed point over a long period of time. Early photographic processes also had limitations. The daguerreotype
Daguerreotype
The daguerreotype was the first commercially successful photographic process. The image is a direct positive made in the camera on a silvered copper plate....
process was far too slow to record anything but the brightest objects, and the wet plate collodion
Collodion
Collodion is a flammable, syrupy solution of pyroxylin in ether and alcohol. There are two basic types; flexible and non-flexible. The flexible type is often used as a surgical dressing or to hold dressings in place. When painted on the skin, collodion dries to form a flexible cellulose film...
process limited exposures to the time the plate could stay wet. The first known attempt at astronomical photography was by Louis Jacques Mandé Daguerre, inventor of the daguerreotype process which bears his name, who attempted in 1839 to photograph the moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot. John William Draper
John William Draper
John William Draper was an American scientist, philosopher, physician, chemist, historian, and photographer. He is credited with producing the first clear photograph of a female face and the first detailed photograph of the Moon...
, an American physician, chemist and scientific experimenter, managed to make the first successful photograph of the moon a year later on March 23, 1840, taking a 20-minute-long daguerreotype
Daguerreotype
The daguerreotype was the first commercially successful photographic process. The image is a direct positive made in the camera on a silvered copper plate....
image using a 5-inch (13 cm) reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
. The first photograph of a star was a daguerreotype of the star Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
by astronomer William Cranch Bond
William Cranch Bond
William Cranch Bond was an American astronomer, and the first director of Harvard College Observatory.- Upbringing :William Cranch Bond was born in Falmouth, Maine on September 9, 1789...
and daguerreotype photographer and experimenter John Adams Whipple
John Adams Whipple
John Adams Whipple was an American inventor and early photographer. He was the first in the United States to manufacture the chemicals used for daguerreotypes; he pioneered astronomical and night photography; he was a prize-winner for his extraordinary early photographs of the moon; and he was the...
, on July 16 and 17, 1850 with Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...
's 15 inch Great refractor
Great refractor
Great refractor refers to a large telescope with a lens, usually the largest refractor at an observatory with an equatorial mount. The preeminence and success of this style in observational astronomy was an era in telescope use in the 19th and early 20th century. Great refractors were large...
.
In 1863 the English chemist William Allen Miller
William Allen Miller
William Allen Miller FRS was a British scientist.He was born in Ipswich, Suffolk and educated at Ackworth School and King's College London....
and English amateur astronomer Sir William Huggins
William Huggins
Sir William Huggins, OM, KCB, FRS was an English amateur astronomer best known for his pioneering work in astronomical spectroscopy.-Biography:...
used the wet collodion plate process to obtain the first ever photographic spectrogram
Spectrogram
A spectrogram is a time-varying spectral representation that shows how the spectral density of a signal varies with time. Also known as spectral waterfalls, sonograms, voiceprints, or voicegrams, spectrograms are used to identify phonetic sounds, to analyse the cries of animals; they were also...
of a star, Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
and Capella
Capella
Capella can refer to:* Capella , a bright star in the constellation of Auriga* Capella , an impact crater on the Moon* Capella, Queensland, a small town in Central Queensland* Capella Island, a minor island of the U.S...
. In 1872 American physician Henry Draper
Henry Draper
Henry Draper was an American doctor and amateur astronomer. He is best known today as a pioneer of astrophotography.-Life and work:...
, the son of John William Draper, recorded the first spectrogram of a star (Vega) to show absorption lines.
Astronomical photography did not become a serious research tool until the late 19th century, with the introduction of dry plate
Dry plate
Dry plate, also known as gelatin process, is an improved type of photographic plate. It was invented by Dr. Richard L. Maddox in 1871, and by 1879 it was so well introduced that the first dry plate factory had been established...
photography. It was first used by Sir William Huggins and his wife Margaret Lindsay Huggins
Margaret Lindsay Huggins
Margaret Lindsay, Lady Huggins , born Margaret Lindsay Murray, was an Irish scientific investigator and amateur astronomer. With her husband William Huggins she was a pioneer in the field of spectroscopy....
, in 1876, in their work to record the spectra of astronomical objects. In 1880 Henry Draper used the new dry plate process with an 11-inch (28 cm) refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...
to make a 51-minute exposure of the Orion Nebula
Orion Nebula
The Orion Nebula is a diffuse nebula situated south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light...
, the first photograph of a nebula ever made. A breakthrough in astronomical photography came in 1883, when amateur astronomer Andrew Ainslie Common
Andrew Ainslie Common
Andrew Ainslie Common FRS was an English amateur astronomer best known for his pioneering work in astrophotography.-Biography:...
used the dry plate process to record several images of the same nebula in exposures up to 60 minutes with a 36-inch (91 cm) reflecting telescope that he constructed in the backyard of his home in Ealing, outside London. These images for the first time showed stars too faint to be seen by the human eye.
1887 saw the Astrographic Catalogue and Carte du Ciel
Carte du Ciel
The Carte du Ciel and the Astrographic Catalogue were two distinct but connected components of a massive international astronomical project, initiated in the late 19th century, to catalogue and map the positions of millions of stars as faint as 11th or 12th magnitude...
, the first all-sky photographic astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
project. It was conducted by 20 observatories all using special photographic telescopes with a uniform design called normal astrograph
Astrograph
An astrograph is a telescope designed for the sole purpose of astrophotography. Astrographs are usually used in wide field surveys of the night sky as well as detection of objects such as asteroids, meteors, and comets.-Design:...
s, all with an aperture of around 13 inches (330 mm) and a focal length of 11 feet (3.4 m), designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm while covering a 2° × 2° field of view. The attempt was to accurately map the sky down to the 14th magnitude
Magnitude (astronomy)
Magnitude is the logarithmic measure of the brightness of an object, in astronomy, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths.-Background:...
but it was never completed.
The beginning of the 20th century saw the worldwide construction of refracting telescopes and sophisticated large reflecting telescopes specifically designed for photographic imaging. Towards the middle of the century, giant telescopes such as the 200-inch (5 meter) Hale Telescope
Hale telescope
The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...
and the 48-inch Samuel Oschin telescope
Samuel Oschin telescope
The Samuel Oschin telescope is a 48-inch aperture Schmidt camera at the Palomar Observatory in northern San Diego County, California. It consists of a 49.75-inch Schmidt corrector plate and a 72-inch mirror. The instrument is strictly a camera; there is no provision for an eyepiece to look...
at Palomar Observatory
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
were pushing the limits of film photography.
Some progress was made in the field of photographic emulsions and in the techniques of forming gas hypersensitization
Forming gas
Forming gas is a mixture of hydrogen and nitrogen. It is sometimes called a "dissociated ammonia atmosphere" due to the reaction which generates it:...
, cryogenic cooling, and light amplification, but starting in the 1970s after the invention of the CCD, photographic plates have given way to electronic imaging in professional observatories. CCD's are far more light sensitive, do not drop off in sensitivity to light over long exposures the way film does ("reciprocity failure"), have the ability to record in a much wider spectral range, and simplify storage of information. Telescopes now use many configurations of CCD sensors including linear arrays and large mosaics of CCD elements equivalent to 100 million pixels, designed to cover the focal plane of telescopes that formerly used 10-to-14-inch photographic plates.
The late 20th century saw advances in astronomical imaging take place in the form of new hardware, with the construction of giant multi-mirror and segmented mirror
Segmented mirror
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric . They are used as objectives for large reflecting telescopes...
telescopes. It would also see the introduction of space based telescopes, such as the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
. Operating outside the atmosphere’s turbulence, scattered ambient light and the vagaries of weather allows the Hubble Space Telescope, with a mirror diameter of 2.4 m, to record stars down to the 30th magnitude, some 100 times dimmer than what the 5-meter Mount Palomar Hale telescope could record in 1949.
Amateur astrophotography
Astrophotography is a popular hobby among photographers and amateur astronomers. Images of the night sky can be obtained with the most basic film and digital cameras. For simple star trails, no equipment may be necessary other than common tripods. There is a wide range of commercial equipment geared toward basic and advanced astrophotography. Amateur astronomers and amateur telescope makers also use homemade equipment and modified devices.Media
Images are recorded on many types of media and imaging devices including single-lens reflex cameraSingle-lens reflex camera
A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...
s, 35 mm film
35 mm film
35 mm film is the film gauge most commonly used for chemical still photography and motion pictures. The name of the gauge refers to the width of the photographic film, which consists of strips 35 millimeters in width...
, digital single-lens reflex camera
Digital single-lens reflex camera
Most digital single-lens reflex cameras are digital cameras that use a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera....
s, simple amateur-level and professional-level commercially manufactured astronomical CCD cameras, video camera
Video camera
A video camera is a camera used for electronic motion picture acquisition, initially developed by the television industry but now common in other applications as well. The earliest video cameras were those of John Logie Baird, based on the electromechanical Nipkow disk and used by the BBC in...
s, and even off-the-shelf webcam
Webcam
A webcam is a video camera that feeds its images in real time to a computer or computer network, often via USB, ethernet, or Wi-Fi.Their most popular use is the establishment of video links, permitting computers to act as videophones or videoconference stations. This common use as a video camera...
s adapted for long-exposure imaging.
Conventional over-the-counter film has long been used for astrophotography. Film exposures range from 10 minutes to over an hour. Commercially available color film stock is subject to reciprocal failure
Reciprocity (photography)
In photography reciprocity refers to the inverse relationship between the intensity and duration of light that determines the reaction of light-sensitive material. Within a normal exposure range for film stock, for example, the reciprocity law states that the film response will be determined by the...
over long exposures, in which sensitivity to light of different wavelengths appears to drop off as the exposure time increases, leading to color shift in the image. This is compensated for by using the same technique used in professional astronomy of taking photographs at different wavelengths that are then combined to create a correct color image. Since film is much slower than digital sensors, tiny errors in tracking can be corrected without much noticeable effect on the final image. Film astrophotography is becoming less popular due to the general spread of low-cost digital cameras and a diminishing supply of suitable film emulsions. Also, film requires continuous on-going costs (film, processing, printing or scanning).
Since the late 1990s amateurs have been following the professional observatories in the switch from film to digital CCDs for astronomical imaging. CCDs are more sensitive than film, allowing much shorter exposure times, and have a linear response to light. Images can be captured in many short exposures to create a synthetic long exposure. Digital cameras also have minimal or no moving parts and the ability to be operated remotely via an infrared remote or computer tethering, limiting vibration. Simple digital devices such as webcam
Webcam
A webcam is a video camera that feeds its images in real time to a computer or computer network, often via USB, ethernet, or Wi-Fi.Their most popular use is the establishment of video links, permitting computers to act as videophones or videoconference stations. This common use as a video camera...
s can be modified to allow access to the focal plane and even (after the cutting of a few wires), for long exposure
Exposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
photography. Digital video cameras are also used. There are many techniques and pieces of commercially manufactured equipment for attaching digital single-lens reflex cameras and even basic point and shoot cameras to telescopes. Consumer level digital cameras suffer from image noise
Image noise
Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera...
over long exposures, so there are many techniques for cooling the camera, including cryogenic
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...
cooling. Astronomical equipment companies also now offer a wide range of purpose-built astronomical CCD cameras complete with hardware and processing software.
Post-processing
Both digital camera images and scanned film images are usually adjusted in image processingDigital image processing
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
software to improve the image in some way. Images can be brightened and manipulated in a computer to adjust color and increase the contrast. More sophisticated techniques involve capturing multiple images (sometimes thousands) to composit together in an additive process to sharpen images to overcome poor atmospheric seeing, negating tracking issues, bringing out faint objects with a poor signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
, and filtering out light pollution. Digital camera images may also need further processing to reduce the image noise
Image noise
Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera...
from long exposures, including subtracting a “dark frame”
Dark frame subtraction
In digital photography, dark-frame subtraction is a way to minimize image noise for pictures taken with long exposure times. It takes advantage of the fact that a component of image noise, known as fixed-pattern noise, is the same from shot to shot: noise from the sensor, dead or hot pixels...
and a processing called image stacking or "Shift-and-add
Shift-and-add
The shift-and-add method is a form of speckle imaging commonly used for obtaining high quality images from a number of short exposures with varying image shifts. It has been used in astronomy for several decades, and is the basis for the image-stabilisation feature on some cameras...
". There are several commercial and freeware
Freeware
Freeware is computer software that is available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Freeware is in contrast to commercial software, which is typically sold for profit, but might be distributed for a business or commercial purpose in the...
software packages available specifically for astronomical photographic image manipulation.
Hardware
Astrophotographic hardware among non-professional astronomers varies widely, since the photographers themselves range from general photographers shooting some form of aesthetically pleasing images to very serious amateur astronomers collecting data for scientific research. As a hobby, astrophotography has many challenges that have to be overcome that differ from conventional photography and from what is normally encountered in professional astronomy. Since most people live in urban areas, equipment needs to be portable so that it can be taken far away from the lights of major cities or towns to avoid urban light pollutionLight pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
. Urban astrophotographers use special light-pollution filters and advanced computer processing techniques to remove ambient urban light from the background of their images. They may also stick to imaging bright targets like the moon and planets. Another method used by amateur astronomers to avoid light pollution is to set up, or rent time, on a remotely operated telescope at a dark sky location. Other challenges include setup and alignment of portable telescopes for accurate tracking, working within the limitations in “off the shelf” equipment, the endurance of monitoring equipment, and sometimes manually tracking astronomical objects over long exposures in a wide range of weather conditions.
Equipment setups
Fixed or tripodThe most basic types of astronomical photographs are made with standard cameras and photographic lenses mounted in a fixed position or on a tripod. Foreground objects or landscapes are sometimes composed in the shot. Objects imaged are constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s, interesting planetary configurations, meteors, and bright comets. Exposure times must be short (under a minute) to avoid having the stars point image become an elongated line due to the Earth's rotation. Camera lens focal lengths are usually short, as longer lenses will show image trailing in a matter of seconds. Allowing the stars to intentionally become elongated lines in exposures lasting several minutes or even hours, called “Star trails”, is an artistic technique sometimes used.
Tracking mounts
To achieve longer exposures without objects being blurred, some form of tracking mount is usually employed to compensate for the Earth's rotation, including commercial equatorial mounts and homemade equatorial devices such as barn door tracker
Barn door tracker
A barn door tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for the observation or photography of astronomical objects. It is a simple alternative to attaching a camera to a motorized equatorial mount.-History:The barn door tracker was...
s and equatorial platform
Equatorial platform
An equatorial platform or equatorial table is an equatorial telescope mount in the form of a specially designed platform that allows any device sitting on it to track astronomical objects in the sky on an equatorial axis. They are used to give equatorial tracking to any device sitting on them, from...
s.
"Piggyback" photography
Piggyback astronomical photography is a method where a camera/lens is mounted on an equatorially mounted astronomical telescope. The telescope is used as a guide scope to keep the field of view centered during the exposure. This allows the camera to use a longer exposure and/or a longer focal length lens or even be attached to some form of photographic telescope co-axial with the main telescope.
Telescope focal plane photography
In this type of photography the telescope itself is used as the "lens" collecting light for the film or CCD of the camera. Although this allows for the magnification and light gathering power of the telescope to be used, it is one of the most difficult astrophotography methods. This is because of the difficulties in centering and focusing sometimes very dim objects in the narrow field of view, contending with magnified vibration and tacking errors, and the added expense of equipment (such as sufficiently sturdy telescope mounts, camera mounts, camera couplers, off axis guiders, guide scopes, illuminated cross-hairs, or auto-guiders mounted on primary telescope or the guide-scope.) There are several different ways cameras (with removable lenses) are attached to amateur astronomical telescopes including:
- Prime focus – In this method the image produced by the telescope falls directly on the film or CCD with no intervening optics or telescope eyepiece.
- Positive projection – A method in which the telescope eyepieceEyepieceAn 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 so 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...
(eyepiece projection) or a positive lens (placed after the focal plane of the telescope objective) is used to project a much more magnified image directly onto the film or CCD. Since the image is magnified with a narrow field of view this method is generally used for lunar and planetary photography. - Negative projection – This method, like positive projection, produces a magnified image. A negative lens, usually a BarlowBarlow lensThe Barlow lens, named for its creator, the English engineer Peter Barlow, is a diverging lens which, used in series with other optics in an optical system, increases the effective focal ratio of an optical system as perceived by all components after it in the system...
or a photographic teleconverterTeleconverterA teleconverter is a secondary lens which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image obtained by the objective lens...
, is placed in the light cone before the focal plane of the telescope objective. - Compression – Compression uses a positive lens (also called a focal reducer), placed in the converging cone of light before the focal plane of the telescope objective, to reduce overall image magnification. It is used on very long focal length telescopes, such as MaksutovMaksutov telescopeThe Maksutov is a catadioptric telescope design that combines a spherical mirror with a weakly negative meniscus lens in a design that takes advantage of all the surfaces being nearly "spherically symmetrical". The negative lens is usually full diameter and placed at the entrance pupil of the...
s and Schmidt–Cassegrains, to obtain a wider field of view.
When the camera lens is not removed (or cannot be removed) a common method used is afocal photography
Afocal photography
Afocal photography, also called afocal imaging or afocal projection is a method of photography where the camera with its lens attached is mounted over the eyepiece of another image forming system such as a optical telescope or optical microscope, with the camera lens taking the place of the human...
, also called afocal projection. In this method both the camera lens and the telescope eyepiece are attached. When both are focused at infinity the light path between them is parallel (afocal
Afocal system
In optics an afocal system is an optical system that produces no net convergence or divergence of the beam, i.e. has an infinite effective focal length. This type of system can be created with a pair of optical elements where the distance between the elements is equal to the sum of each element's...
), allowing the camera to basically photograph anything the observer can see. This method works well for capturing images of the moon and brighter planets, as well as narrow field images of stars and nebulae. Afocal photography was common with early 20th century consumer level cameras, since many models had non-removable lenses. It has grown in popularity with the introduction of point and shoot digital cameras since most models also have non-removable lenses.
Remote Telescope Astrophotography
With the development of fast Internet in the last part of the 20th century along with advances in computer controlled telescope mounts and CCD cameras 'Remote Telescope' astronomy is now a viable means for amateur astronomers not aligned with major telescope facilities to partake in research and deep sky imaging. This enables the imager to control a telescope a large distance away in a dark location. The observers can image through the telescopes using CCD cameras.Imaging can done regardless of the location of the user or the telescopes they wish to use. The digital data collected by the telescope is then transmitted and displayed to the user by means of the Internet. An example of a digital remote telescope operation for public use via the Internet is The Bareket Observatory
Bareket observatory
The Bareket Observatory is an astronomical educational observatory owned and operated by the Bareket family. It is located east of the city of Maccabim, near Modiin....
.
See also
- AstrographAstrographAn astrograph is a telescope designed for the sole purpose of astrophotography. Astrographs are usually used in wide field surveys of the night sky as well as detection of objects such as asteroids, meteors, and comets.-Design:...
- Canon EOS 20Da
- David MalinDavid MalinDavid Malin is a British-Australian astronomer and photographer.Malin trained as a chemist and originally worked in England as microscopist...
- DigiscopingDigiscopingDigiscoping is a neologism for the activity of using a digital camera to record distant images by coupling it with an optical telescope. The term usually refers to using either a digital single-lens reflex camera with lens attached or, more often, a fixed lens point and shoot digital camera to...
- Edward Emerson Barnard
- Isaac RobertsIsaac RobertsIsaac Roberts was a Welsh engineer and business man best known for his work as an amateur astronomer, pioneering the field of astrophotography of nebulae. He was a member of the Liverpool Astronomical Society in England and was a fellow of the Royal Geological Society...
- Light pollutionLight pollutionLight pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
- Max WolfMax WolfMaximilian Franz Joseph Cornelius Wolf was a German astronomer and a pioneer in the field of astrophotography...
- Montage Image Mosaic SoftwareMontage Image Mosaic SoftwareMontage is a software toolkit used in astronomy to assemble astronomical images in Flexible Image Transport System format into composite images, called mosaics, that preserve the calibration and positional fidelity of the original input images. It won a NASA Space Act Award in 2006...
- National Geographic Society – Palomar Observatory Sky SurveyNational Geographic Society – Palomar Observatory Sky SurveyThe National Geographic Society – Palomar Observatory Sky Survey is a major photographic survey of the night sky that was completed at Palomar Observatory in 1958.-Observations:...
- Night photographyNight photographyNight photography refers to photographs taken outdoors between dusk and dawn. Night photographers generally have a choice between using artificial light and using a long exposure, exposing the scene for seconds, minutes, and even hours in order to give the film or digital sensor enough time to...
- Schmidt cameraSchmidt cameraA Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
Further reading
- http://books.google.com/books?id=VYyldcYfq3MC&pg=PA508&lpg=PA508&dq=astrophotography+%22professional+astronomers%22&source=bl&ots=sYsdxtKm8S&sig=tetwY1OgHcgsaHL0ul-lBLMNavc&hl=en&ei=SL-GS9bVDc6JlAfLgLXVCw&sa=X&oi=book_result&ct=result&resnum=7&ved=0CBkQ6AEwBjge#v=onepage&q=astrophotography%20%22professional%20astronomers%22&f=falseFocal encyclopedia of photography: digital imaging, theory and applications by Michael R. Peres, page 508 - Astrophotography]
- Wikibooks - Digital camera astrophotography
- WikiHOW - How to Photograph the Night Sky (Astrophotography)
External links
- Henry Draper's Photograph of the Moon, 1863 on Cyanotype
- The Early History of Astrophotography
- The History of Astrophotography
- CCD's Versus Professional Plate Film - by Ricky Leon Murphy
- Astrophotography - The Amateur Connection, The Roles of Photography in Professional Astronomy, Challenges and Changes
- WebCam Astrophotography with Amateur Telescopes