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ASTROPHOTOGRAPHY WITH A DSLR
Astrophotography with a DSLR
Whether you are an experienced photographer wishing to have a go at astronomy or an astronomer
wanting to photograph a few favourite objects, it is amazing what you can do with a DSLR, even
without a telescope. If you need guidance on navigating the night sky, check out Further
You could easily be forgiven for thinking that astrophotography is an expensive hobby. Certainly, 15
years ago, it was true. I started by borrowing my wifes compact digital camera at the end of 2003. I
started off with the Moon and have owned a succession of my own since. Initially, I took photos of
bright objects, like the Sun, Moon and brighter planets by holding a camera to a telescope eyepiece.
Over the years, I pushed the boundaries of this technology to the limits and found that even a simple
compact digital camera can capture stellar constellations. I was limited to an exposure time of 8
seconds as I did not have a driven telescope of camera mount. In fact, I still do not have one today.
I felt quite pleased with what I could do with 8 seconds but always thought imagine what I could do
with 30. My wish came true in 2013 when I pooled a few cash presents for Christmas to buy a
second-hand DSLR. I was certainly able to photograph constellations and was particularly pleased
when I caught the scorpions tail on film for the first time.
Fig 1 Scorpius
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This is quite a pot for a UK-based astronomer as the tail never rises above the horizon even from
Southern England. I was on a business trip to Aruba in the Caribbean. Conditions were quite poor on
the day, due to a lot of haze on the horizon but could capture the main stars.
Apart from needing to travel far enough south to see Scorpius, the great thing about this photo is
that anyone can do it. A bit of digital wizardry works, too but the constellation can be recognised
from the original image.
The Basics You can skip this bit if you have already used a DSLR camera. In a nutshell, DSLR stands for Digital
Single Lens Reflex. Lenses are interchangeable and most cameras are supplied with a single zoom
lens, with a variable focal length, usually around 18mm to 55mm. A short focal length gives you a
wide field of view and brighter image, whereas a longer focal length gives you a closer view but a
fainter image. It follows that you would normally use a short focal length for large, faint objects,
such as constellations and a long focal length for small, bright objects, such as the Moon.
A DSLR also allows you to adjust the brightness of the image and is given by the ISO number, which
usually ranges from 100 to 3200, with the higher number being brighter. You can use automatic
settings, although I do not recommend this for astronomical use, as most cameras are designed for
photographing people and scenery.
You can also adjust the exposure setting, usually from 1/4000 second to 30 seconds. Like the
brightness settings, you can use automatic mode. There is also bulb mode where you can control
the exposure time manually but this is best left until you have more practice.
You can also focus a DSLR automatically but, again, manual settings are better for astronomical use.
However, some objects are difficult to focus on and need a lot of patience and experience.
For most DSLR cameras, it is possible to buy additional lenses, such as a zoom lens from 70mm to
300mm focal length. Fixed focal length lenses are available but are often expensive and less
For basic information on DSLRs see Further Information.
Constellations It would follow that to photograph constellations, you would use a short focal length, the maximum
brightness setting that your camera allows and a very long exposure. Unfortunately, not. Earths
rotation means that everything moves across the sky and blurs if the exposure is too long. Another
factor is that, even an apparently pitch black sky is never completely dark.
The solution is to use an exposure time of 30 seconds, 18mm (or shorter) focal length and a
brightness setting of 800. If there are lots of street lights around or the Moon is about, reduce this to
400 and use 1600 if you are well away from artificial light.
You can increase the exposure time if the constellation is nearer the celestial pole (near Polaris in
the northern hemisphere, near Sigma Octanis in the southern hemisphere). About halfway between
the celestial equator and the pole, you can use an exposure of about 42 seconds and about 3
minutes at the pole itself. This is because constellations rotate more slowly in the polar regions.
Ideally, you need a tripod to steady the camera but I have even been known to balance a camera on
the top of a car or a park bench.
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ASTROPHOTOGRAPHY WITH A DSLR
A favourite target amongst astrophotographers is Orion. I have even taken half-decent shots of it
using a compact digital camera.
Fig 2 Orion
This Orion shot shows a lot of what is good about the method and one problem. Many of the stars
visible were too faint to see from where I took the shot from (suburbia). The scale is large enough to
show the full constellation and parts of the neighbouring ones. You can see the Hyades and Pleiades
(star clusters) on the upper right. The problem with constellations near the horizon is that there is
more atmosphere between the camera and the stars and that usually means more haze. This often
produces a red background glow in the lower part of the photo. You can work around this by
photographing constellations higher in the sky and one of my favourite shots is to capture the zenith
by laying a camera on its back.
It is possible to obtain a photograph like Fig 2 without doing anything special, but I created it using a
technique known as stacking. You can read more about it here: Philip Pugh's Website: Phil's
Scribblings: Stacking. This combines detail from several individual photographs into one.
Another of my favourite constellations is Perseus. Fig 3 shows the neighbouring constellation of
Auriga and parts of Taurus, too. I would almost say it is too good, as the pattern of the constellation
seems lost in the stellar background.
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Fig 3 Perseus
About losing constellations in the stellar background, you can capture the Milky Way with this set-
up, too. From the northern hemisphere, the area around Cygnus and Lyra is particularly attractive.
Those of you who live in the southern hemisphere or south of the Tropic of Cancer should try this
with the galactic centre.
Fig 4 Milky Way
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ASTROPHOTOGRAPHY WITH A DSLR
You can capture most of the small constellations but they are often swamped by larger, brighter
constellations in the same photograph. One way to work around this is to use a longer focal length
lens and a shorter exposure time. For example, you can use a 10 second exposure for a small
constellation near the celestial equator. Fortunately, you can counteract this, to some extent, by
increasing the brightness setting. To really show the constellation at its best, you can use stacking to
capture more stars.
Fig 5 Lyra
This photo was taken with a brightness setting of ISO 6400, 8 seconds exposure and a focal length of
100mm (using another zoom lens). Note that I could use a longer exposure, as Lyra is just under half-
way between the celestial equator and celestial pole. I stacked the best 9 of 14 images using the
Deep Sky Stacker tool. The close-up of Lyra also increases the distance between stars, so you can see
the double stars Epsilon and Delta Lyrae. Each component of Epsilon Lyrae is also a double star but
requires a longer focal length than most camera lenses have.
Although Ive seen it written that people dont do constellations any more, I find that
photographing them is a fascinating branch of the hobby. There are still many constellations, even in
the northern hemisphere that I have not photographed yet and even more where I feel I could take
better photographs than I already have. Although it is possible to photograph constellations when
the Moon or light cloud is around, you can get the best results on clear, moonlit nights. If you can
photograph objects from a dark site, free of artificial light, even better. Having said that, most of my
photographs are taken from suburbia. A good test is to see whether you can see the Milky Way. If
so, you are in business.
I recommend that you start off with large constellations with many stars of 3rd magnitude or
brighter. Apart from the constellations I have shown, others worth trying are:
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Widefield astrophotography can be used to capture events that are not suitable for capture by
telescopes. Meteors can be captured purely by accident or deliberately during major showers. The
International Space Station appears as a bright tra