Astrophotography with a DSLR - Philip Pugh's with a DSLR.pdfP a g e | 1 ASTROPHOTOGRAPHY WITH A DSLR Astrophotography with a DSLR Introduction Whether you are an experienced photographer

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  • P a g e | 1

    ASTROPHOTOGRAPHY WITH A DSLR

    Astrophotography with a DSLR

    Introduction

    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

    Information.

    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

    versatile.

    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.

    http://www.philippughastronomer.com/PhilsScribblings_Stacking.htmlhttp://www.philippughastronomer.com/PhilsScribblings_Stacking.html

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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:

    Ursa Major

    Cygnus

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    Taurus

    Gemini

    Aquila

    Leo

    Trails

    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

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