Astrophotography is a photography taking constellations, the moon, the sun, etc. as the shooting objects.Astronomical photography is a special photography technology, which can record various celestial bodies andCelestial phenomena, MoonplanetEven remotedeep space 。Astronomical photography does not have to be carried out at night. Some special astronomical phenomena such assolar eclipseYou need to shoot during the day.The required equipment varies according to the shooting object, which is as simple as one setStandard lensOfSingle mirror reflector（SLR，single lens reflex camera），Complex as cooling connected to telescopeCCD camera, can shoot.In addition to the observatory, there are a large number of astronomy enthusiasts all over the world who actively participate in this activity, even regard it as an interest.
With the popularity of digital cameras in the past decade, and the leap in related image processing and capture technologies, quite a few fans of traditional films have turned to digital light-sensitive equipment cameras as tools for astronomical photography. The image presented is also much better than traditional films in terms of clarity and sense of hierarchy. Digital astronomical photography has also become one of the mainstream astronomical photography projects.
A successful astronomical photograph has certain appreciation value, and some works can be used for scientific research.For example, meteor shower photos can be used by astronomers to calculate the exact location of meteor shower radiation points, and some supernova explosions are even recorded inphotosensitiveThe board has been recognized by scholars for many years.
advantage
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objectivity
Before the appearance of astronomical photography, visual description became the only recording method other than text description.However, the description has subjective shortcomings.For the same observation object, different people will draw different results.Astronomical photography is more objective.In addition, it can record many data of celestial bodies at the same time, includingluminosity, color, etc.
Enhanced observation of dim and weak objects
Galaxies NGC 5426 and NGC 5427 in Virgo
In the past, observation could only be achieved with naked eyes and telescopes.However, a large number of celestial bodies are still invisible to the naked eye, partly because of the extremely dim relationship, and the other reason is that the naked eye cannot see electromagnetic waves outside the visible spectrum.For the formertime exposureLight from dim celestial bodies can be accumulated on photosensitive elements (traditional negative or photoelectric coupling elements).In general, the longer the exposure time, the more dim objects can be recorded.As for taking electromagnetic waves beyond the visible spectrumPhotosensitive materialYou can record all kinds of radiation of celestial bodies.Shooting the same object at different wavelengths can observe various details of the object.
Difference from daily photography
Since most of the objects photographed are very dim, astronomical photography requires a long exposure time.In addition, the choice of shooting location is very important.Astronomical photography in cities with serious light damage will be more difficult, and the results will not be ideal.Astronomers will go to places far away from the city, such as mountains, to take photos.The weather is a major factor in the possibility of shooting.Mist and clouds are enough to make shooting impossible.Even if the meteorological department can predict the weather conditions, it cannot or will not predict the change of cloud cover.Temperature has an impact on equipment and photographers. Low temperature will drain the battery early and affect camera operation;Prolonged exposure to cold air is enough to frostbite the photographer.
Special equipment may be used during shooting.However, as far as the performance requirements of cameras are concerned, astronomical photography has much lower performance requirements than daily photography.
Astronomical photography can be a challenge to physical strength and knowledge.Astronomical photography is often carried out at night and stays up late for a long time.Equipment handling is another arduous task.Some equipment such asAstronomical telescopeIt is often not light, and the shooting location is far away from light damage, so it needs to choose a remote location, and the transportation tools may not be able to reach directly.The photographer may have to drive to the shooting location before moving the equipment.To take astronomical photos, the photographer needs some astronomical knowledge.For example, you should be familiar with the location and occurrence of celestial bodies and the shooting method.
Setting goals too high is often the source of failure, especially the photographer himself does not have the necessary knowledge and technology;High expectations are often the reason for giving up, especially the photographer's unrealistic fantasies about the photos;But the joy of success is incomparable.
Camera Equipment
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camera
An example of Olympus OM-2: 135 single mirror reflector
Astronomical photography does not necessarily need astronomical telescopes, as simple as a camera mounted on a tripod can already take photos.In terms of cameras, from 135 single mirror reflectors to 6x9 large negative cameras, astronomical photography can be done.However, a camera suitable for photographing various celestial bodies and astronomical phenomena should have the following characteristics:
With multi-stage shutter and B (Bulb) shutter, the lens can be replaced with long exposure and the telescope can be connected with light weight. In view of the above conditions, 135 single mirror reflector is the most suitable for all kinds of astronomical photography.It is better to purchase a shutter cable with a lock catch to reduce vibration interference, or replace the B or T gate for long-term exposure.
negative
In terms of film, low-speed film such as ISO 25 can be selected if the sun is photographed.For shooting the moon, solar eclipse or lunar eclipse, medium and high speed films with ISO 100 to 400 degrees can be used.While shooting Xingyethe galaxy, nebulae, galaxies or comets can use ISO 400 high-speed film or even ISO 3200 high-speed film.In terms of color negatives suitable for astronomical photography, the positive films include Kodak Ektachome E200 and Fuji Provia 400F, and the negative films include Kodak Ektapress 800 and Fuji Press 800.Black and white negatives include Kodak T-MAX 400 and T-MAX P3200.
Photography
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The way of taking astronomical photos varies from subject matter to subject matter, but can be classified into three categories:Fixed photography、Tracking photographyandMagnification photography。
Fixed photography
Star tracks taken by fixed photography
Fixed photography can be said to be the simplest astronomical photography method. It does not need a telescope, but basically only needs a camera and a tripod.Sometimes a cable release is used.Most cameras can be used for fixed photography. It is important that the camera can be exposed for a long time (more than 1 second).Among them, withB Shutter135 single mirror reflector is most suitable. If it is matched with the shutter cord (and can be locked automatically when pressed), it can be exposed in hours.Some single mirror reflectors can operate the B shutter without batteries, such as the famous Nikon FM2.During hours of exposure, a camera using an electronic shutter consumes considerable power.If the power is exhausted, the shutter will close and the exposure will be aborted.As for general digital cameras, the slowest shutter is only a few seconds to one minute, and you can take some constellation photos.If you want to shoot star trails, single mirror reflection is more appropriate.
Camera performance requirements are not high.Light meter, auto focus, auto exposure and auto film transfer are not required.Of course, these functions are still needed when photographing solar eclipses.However, when shooting objects such as constellations, star trails and meteor showers, these functions are not useful.
Almost all single mirror reflectors can change the lens for the purpose of visual shooting.As long as the aperture of the lens is not too small.Lensfocal lengthThe smaller the value, the wider the field of view, and the larger the range of sky area that can be photographed.Some people suggest that novices useStandard lens, because its price is generally cheaper and its quality is generally good.Fixed focus lensThe optical quality of zoom lens is generally better than that of zoom lens.
When shooting, fix the camera on the tripod first, and make sure that the focus is at infinity (marked as ∞ on the lens) when focusing.It should be noted that the infinity mark of some auto focus lenses does not match the real infinity position.Set the shutter to B, face the sky area to be photographed, and press the shutter to expose.
There are many objects that can be photographed in fixed photography, such as constellations, star tracks, solar/lunar eclipses, meteors and even auroras.
It only takes 5 to 30 seconds of exposure to shoot bright planets and constellations with fixed photography.When shooting, please open the aperture of the lens to the maximum (or narrow down one level), and the lens is from fishglasses toStandard lensBoth.If the environment permits, try ISO 800, 1600 or even 3200.Users of digital cameras can take a trial photo to see the effect before taking official photos, and then take photos with different exposure combinations.Due to the constant rotation of the star sky from east to west, the exposure time must be limited if the star is to be kept in point shape;See here for exposure time limit.
Tracking photography
Use equatorial instrument to track, photograph and stack
Tracking photography is also called tracking photography.Because of the rotation of the earth itselfDiurnal visual movement。From the above photo of fixed photography, we can know that when the fixed exposure time of the camera is long enough, the stars will pull lines, so that clear stars cannot be formed.In fact, no matter how long the time is, there will be a certain degree of pulling, but if the time is very short, there will be no pulling phenomenon.The exposure time can be very short when shooting brighter objects, such as the sun and moon;However, if you want to photograph weaker objects, such as nebulae and galaxies in the deep sky, you must extend the exposure time so that the photosensitive system can collect enough starlight and show it.If you want to get an astronomical photographic work with clear star points and no line, you need an instrument to offset the diurnal apparent motion by rotating in the opposite direction to the rotation of the earth when the exposure time is enough.We call this instrument "equatorial instrument".Generally, the equatorial instrument is divided into German equatorial instrument and Japanese equatorial instrument.General requirements for tracking photographyGuide starThis is a technology that is called two difficult points of astronomical photography together with focusing.It generally needs to have afocal lengthLong lens, through detecting the image in the lens, the guided star is always in thefieldThe same point inside, which can accurately offset the visual movement.In recent years, the electronic and automated technology makes it unnecessary for tracking photography to follow the guide star forever. Many modern equatorial instruments can already be connected to computers, and can be controlled through software or network to achieve the purpose of accurate operation of equatorial instruments.The world's leading manufacturers in the technical development of equatorial instruments include Takahashi, Meade, Celestron and Vixen.Many of their products have high accuracy and convenience. In particular, the equatorial instrument of Gaoqiao has become the most popular equatorial instrument product for astronomers all over the world, and has become an industry indicator. Astronomers are proud to have the products of the above famous manufacturers (not only the equatorial instrument).
Magnification photography
Amplification photography, like straight focus photography, belongs to tracking photography, but the exposure time is relatively short.However, magnification photography is subject to great external influence, which is the worst photography method among all astronomical photography.
Equipment for magnification photography
The equipment for magnifying photography and the equipment for straight focus photography are very repetitive.But magnifying photography is not necessaryGuide starYou can save a sum of money on guiding star equipment, and you can also buy an additional adapter for magnifying photography.
Telescope: any type of telescope (preferably large aperture, long focal length), high-precision equatorial instrument
Other relevant accessories: magnifying camera cylinder, eyepiece for magnifying projection, recording equipment
Of course, the bigger the telescope, the better. This is the truth, and the longer the focal length is, the easier it is to increase the magnification.In addition, magnifying photography requires the use of eyepieces to magnify the image of celestial bodies. The eyepiece used for magnifying photography is different from the general eyepiece. The quality of the eyepiece shot with the special eyepiece for magnifying and projection is better, but the price of the eyepiece is relatively high.
1. Enlarge the photographic object
Enlarged photography is mainly used to take pictures of parts of the planet, the sun and the moon, such as sunspots or a crater on the moon.This is because the apparent diameter of the planet is very smallfocal lengthThe planet in the photo will be too small to see the surface of the planet, so it is necessary to magnify the image of the planet with an eyepiece to see the appearance or changes of the planet surface.However, some people used low power eyepiece to take photosPlanetary nebulaThis is mainly due to the insufficient focal length of the telescope, and the nebula is too small.This kind of shooting is quite difficult, and it is difficult to shoot well without considerable experience.
2. Method of magnification photography
The previous preparations for magnification photography are the same as those for straight focus photography. The instrument is mounted first (it can be omittedGuide starEquipment), balance, align the positive axis, find the target, and press the shutter after the shooting and light measurement.The only difference from the straight focus photography is the camera mounting method. The camera is not directly mounted with a telescope.Between the telescope and the camera, there must be an adapter that can connect the two and mount the eyepiece. The author calls it the magnifying camera adapter.After the telescope, first connect the magnifying camera receiver, and then connect the camera.Put the low power eyepiece into the receiver, find the object to be photographed, then put on the high power eyepiece, and then focus and measure the light by pressing the shutter.It's easy, isn't it?
3. Problems with magnification photography
If only it were so simple.On the earth, we need air to survive, but this atmosphere seriously interferes with astronomical observation and photography.First, we know two things: First, the disturbance of the air will make the stars shake, causing the picture unclear.2、 A short focal length can see a wide range, while a long focal length can see a narrow range.The reason why magnifying photography needs to be magnified with eyepiece is that the telescopefocal lengthIf it is not long enough, the magnifying function of the eyepiece must be used to extend the focal length.The longer the focal length is, the smaller the viewing range will be, so as long as there is a little air disturbance, it will be obvious in the telescope.Therefore, in order to take a good magnified photograph, one must be able to observe the face of God in addition to strength.
The second problem of magnification photography is the tracking accuracy of the equatorial instrument.As mentioned above, the planet is too small, so you need to use an eyepiece to zoom in (that is, extend the focus).When the magnification is very large, the extended focal length is about tens of thousands of mm. With such a long focal length, if the polar axis of the equatorial instrument is misaligned or the tracking accuracy of the equatorial instrument is not enough, let alone the exposure is only a few seconds, even if it is as short as one second, it will affect the clarity (that is, the resolution) of shooting objects.In addition, the aperture of the telescope suitable for magnifying photography is not small, so an "adequate" equatorial instrument is extremely necessary.
The third problem is strange. It is the vibration - not the vibration of the ground or the telescope, but the vibration of the camera reflector.There is a reflector in the single reflex camera. The reflector will bounce up at the moment of pressing the shutter. This action will cause the camera to shake (or the telescope to shake). The darker the object is, the less sensitive it is to this action, but the impact on the planet or the moon is not small. So if the reflector of the camera can bounce up and lock and then re expose,This kind of camera is more suitable for magnification photography.
The fourth problem is focusing.When we magnify the planet with a high power eyepiece, the planet will become very dark and difficult to focus.In addition to using a brighter focus screen, you can only take more shots to accumulate experience.
One solution to the above problem is to use high sensitivity.We can use four or even eight hundred degree film to shoot the planet or moon surface, still can get good results, and can use high sensitivity to shorten the exposure time, overcomeAtmospheric disturbanceAnd the problem of tracking error can be said to be solved with one stroke.
Astronomical photography generally refers to optical astronomical photography, which can be divided into three aspects in terms of the objects photographed: detailed photography of stars in the solar system, photography of constellations and meteor showers, and photography of deep sky nebulae.
