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 wishing to have a go at astronomy or an

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<ul><li><p>P a g e | 1 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>Astrophotography with a DSLR </p><p>Introduction </p><p>Whether you are an experienced photographer wishing to have a go at astronomy or an astronomer </p><p>wanting to photograph a few favourite objects, it is amazing what you can do with a DSLR, even </p><p>without a telescope. If you need guidance on navigating the night sky, check out Further </p><p>Information. </p><p>You could easily be forgiven for thinking that astrophotography is an expensive hobby. Certainly, 15 </p><p>years ago, it was true. I started by borrowing my wifes compact digital camera at the end of 2003. I </p><p>started off with the Moon and have owned a succession of my own since. Initially, I took photos of </p><p>bright objects, like the Sun, Moon and brighter planets by holding a camera to a telescope eyepiece. </p><p>Over the years, I pushed the boundaries of this technology to the limits and found that even a simple </p><p>compact digital camera can capture stellar constellations. I was limited to an exposure time of 8 </p><p>seconds as I did not have a driven telescope of camera mount. In fact, I still do not have one today. </p><p>I felt quite pleased with what I could do with 8 seconds but always thought imagine what I could do </p><p>with 30. My wish came true in 2013 when I pooled a few cash presents for Christmas to buy a </p><p>second-hand DSLR. I was certainly able to photograph constellations and was particularly pleased </p><p>when I caught the scorpions tail on film for the first time. </p><p>Fig 1 Scorpius </p></li><li><p>Phils Scribblings </p><p>P a g e | 2 </p><p>This is quite a pot for a UK-based astronomer as the tail never rises above the horizon even from </p><p>Southern England. I was on a business trip to Aruba in the Caribbean. Conditions were quite poor on </p><p>the day, due to a lot of haze on the horizon but could capture the main stars. </p><p>Apart from needing to travel far enough south to see Scorpius, the great thing about this photo is </p><p>that anyone can do it. A bit of digital wizardry works, too but the constellation can be recognised </p><p>from the original image. </p><p>The Basics You can skip this bit if you have already used a DSLR camera. In a nutshell, DSLR stands for Digital </p><p>Single Lens Reflex. Lenses are interchangeable and most cameras are supplied with a single zoom </p><p>lens, with a variable focal length, usually around 18mm to 55mm. A short focal length gives you a </p><p>wide field of view and brighter image, whereas a longer focal length gives you a closer view but a </p><p>fainter image. It follows that you would normally use a short focal length for large, faint objects, </p><p>such as constellations and a long focal length for small, bright objects, such as the Moon. </p><p>A DSLR also allows you to adjust the brightness of the image and is given by the ISO number, which </p><p>usually ranges from 100 to 3200, with the higher number being brighter. You can use automatic </p><p>settings, although I do not recommend this for astronomical use, as most cameras are designed for </p><p>photographing people and scenery. </p><p>You can also adjust the exposure setting, usually from 1/4000 second to 30 seconds. Like the </p><p>brightness settings, you can use automatic mode. There is also bulb mode where you can control </p><p>the exposure time manually but this is best left until you have more practice. </p><p>You can also focus a DSLR automatically but, again, manual settings are better for astronomical use. </p><p>However, some objects are difficult to focus on and need a lot of patience and experience. </p><p>For most DSLR cameras, it is possible to buy additional lenses, such as a zoom lens from 70mm to </p><p>300mm focal length. Fixed focal length lenses are available but are often expensive and less </p><p>versatile. </p><p>For basic information on DSLRs see Further Information. </p><p>Constellations It would follow that to photograph constellations, you would use a short focal length, the maximum </p><p>brightness setting that your camera allows and a very long exposure. Unfortunately, not. Earths </p><p>rotation means that everything moves across the sky and blurs if the exposure is too long. Another </p><p>factor is that, even an apparently pitch black sky is never completely dark. </p><p>The solution is to use an exposure time of 30 seconds, 18mm (or shorter) focal length and a </p><p>brightness setting of 800. If there are lots of street lights around or the Moon is about, reduce this to </p><p>400 and use 1600 if you are well away from artificial light. </p><p>You can increase the exposure time if the constellation is nearer the celestial pole (near Polaris in </p><p>the northern hemisphere, near Sigma Octanis in the southern hemisphere). About halfway between </p><p>the celestial equator and the pole, you can use an exposure of about 42 seconds and about 3 </p><p>minutes at the pole itself. This is because constellations rotate more slowly in the polar regions. </p><p>Ideally, you need a tripod to steady the camera but I have even been known to balance a camera on </p><p>the top of a car or a park bench. </p></li><li><p>P a g e | 3 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>A favourite target amongst astrophotographers is Orion. I have even taken half-decent shots of it </p><p>using a compact digital camera. </p><p>Fig 2 Orion </p><p>This Orion shot shows a lot of what is good about the method and one problem. Many of the stars </p><p>visible were too faint to see from where I took the shot from (suburbia). The scale is large enough to </p><p>show the full constellation and parts of the neighbouring ones. You can see the Hyades and Pleiades </p><p>(star clusters) on the upper right. The problem with constellations near the horizon is that there is </p><p>more atmosphere between the camera and the stars and that usually means more haze. This often </p><p>produces a red background glow in the lower part of the photo. You can work around this by </p><p>photographing constellations higher in the sky and one of my favourite shots is to capture the zenith </p><p>by laying a camera on its back. </p><p>It is possible to obtain a photograph like Fig 2 without doing anything special, but I created it using a </p><p>technique known as stacking. You can read more about it here: Philip Pugh's Website: Phil's </p><p>Scribblings: Stacking. This combines detail from several individual photographs into one. </p><p>Another of my favourite constellations is Perseus. Fig 3 shows the neighbouring constellation of </p><p>Auriga and parts of Taurus, too. I would almost say it is too good, as the pattern of the constellation </p><p>seems lost in the stellar background. </p><p></p></li><li><p>Phils Scribblings </p><p>P a g e | 4 </p><p>Fig 3 Perseus </p><p>About losing constellations in the stellar background, you can capture the Milky Way with this set-</p><p>up, too. From the northern hemisphere, the area around Cygnus and Lyra is particularly attractive. </p><p>Those of you who live in the southern hemisphere or south of the Tropic of Cancer should try this </p><p>with the galactic centre. </p><p>Fig 4 Milky Way </p></li><li><p>P a g e | 5 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>You can capture most of the small constellations but they are often swamped by larger, brighter </p><p>constellations in the same photograph. One way to work around this is to use a longer focal length </p><p>lens and a shorter exposure time. For example, you can use a 10 second exposure for a small </p><p>constellation near the celestial equator. Fortunately, you can counteract this, to some extent, by </p><p>increasing the brightness setting. To really show the constellation at its best, you can use stacking to </p><p>capture more stars. </p><p>Fig 5 Lyra </p><p>This photo was taken with a brightness setting of ISO 6400, 8 seconds exposure and a focal length of </p><p>100mm (using another zoom lens). Note that I could use a longer exposure, as Lyra is just under half-</p><p>way between the celestial equator and celestial pole. I stacked the best 9 of 14 images using the </p><p>Deep Sky Stacker tool. The close-up of Lyra also increases the distance between stars, so you can see </p><p>the double stars Epsilon and Delta Lyrae. Each component of Epsilon Lyrae is also a double star but </p><p>requires a longer focal length than most camera lenses have. </p><p>Although Ive seen it written that people dont do constellations any more, I find that </p><p>photographing them is a fascinating branch of the hobby. There are still many constellations, even in </p><p>the northern hemisphere that I have not photographed yet and even more where I feel I could take </p><p>better photographs than I already have. Although it is possible to photograph constellations when </p><p>the Moon or light cloud is around, you can get the best results on clear, moonlit nights. If you can </p><p>photograph objects from a dark site, free of artificial light, even better. Having said that, most of my </p><p>photographs are taken from suburbia. A good test is to see whether you can see the Milky Way. If </p><p>so, you are in business. </p><p>I recommend that you start off with large constellations with many stars of 3rd magnitude or </p><p>brighter. Apart from the constellations I have shown, others worth trying are: </p><p> Ursa Major </p><p> Cygnus </p></li><li><p>Phils Scribblings </p><p>P a g e | 6 </p><p> Taurus </p><p> Gemini </p><p> Aquila </p><p> Leo </p><p>Trails </p><p>Widefield astrophotography can be used to capture events that are not suitable for capture by </p><p>telescopes. Meteors can be captured purely by accident or deliberately during major showers. The </p><p>International Space Station appears as a bright trail against a stellar or twilit background. Fainter </p><p>satellites and aircraft also show as trails. Usually, some break in the trails or lights that appear </p><p>alongside the trails differentiate them from meteors. For most of these types of shots, the camera </p><p>settings are the same as for constellations. For meteors, it is better to use a higher brightness (ISO) </p><p>setting and a shorter exposure time. Ive found my meteor numbers are up since adopting this </p><p>approach and now use ISO 6400 and 5 seconds exposure. </p></li><li><p>P a g e | 7 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p></li><li><p>Phils Scribblings </p><p>P a g e | 8 </p><p>Fig 6 Satellite Trails </p><p>The three photos of Fig 6 clearly identify the object as a satellite. You can see the trail from top left </p><p>to bottom right in successive photos. Both meteors and aircraft are usually faster moving. </p><p>Fig 7 International Space Station </p></li><li><p>P a g e | 9 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>Fig 7 shows a 30 second exposure of an International Space Station trail. Notice that it is near the </p><p>Plough (a.k.a Big Dipper). You can find when the ISS is visible from your location by looking it up on </p><p>the Internet. </p><p>Fig 8 Aeroplane Trails </p><p>Figure 8 shows some star trails. It was a deliberate attempt to take undriven long exposures of stars </p><p>to demonstrate their movement with Earths rotation. It is also a good technique for capturing </p><p>meteors. You need to be able to take exposures of longer than 30 seconds and up to an hour. You </p><p>need to hold the exposure button for a long time or use a remote shutter release (see Accessories, </p><p>below). I recommend a low brightness setting (ISO 400 or less), as the long exposure can brighten </p><p>the background sky quite considerably. You can tell that the tracks are from aircraft due to the dots </p><p>along the trails. </p></li><li><p>Phils Scribblings </p><p>P a g e | 10 </p><p>Fig 9 Meteor Trail </p><p>Fig 9 shows the real thing. Even at high zoom level, the trail is continuous. It is slightly twisted in </p><p>parts but this is reportedly quite common for meteors. I made a blog comment at the time </p><p>suggesting that I could accurately predict the exact appearance and track of meteors but not even </p><p>professional astronomers can do that. Honestly? I just happened to be photographing the right part </p><p>of the sky at the right time. </p><p>So thats it? No not quite. Sometimes you come across something that nobody can easily explain. It </p><p>is quite easy to consider the possibility of little green men. Honestly, whilst I believe that life exists in </p><p>the universe at places other than our planet, Im equally sceptical about Earth being visited by alien </p><p>intelligence. With the object not resembling a meteor trail, it was clearly a rather slow-moving </p><p>object. The presence of the red dots might suggest an aircraft but the slow speed indicates that it </p><p>would be flying very high. The other explanation was a helicopter. </p></li><li><p>P a g e | 11 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>Fig 10 UFO </p><p>The Moon </p><p>Quite honestly, some form of telescope imaging is ideal for lunar astrophotography but you can still </p><p>get some good results with a DSLR given a bit of skill and even more luck. The main difficulty is that </p><p>the Moon comes nowhere near filling the camera field of view, even at long focal length. Also, a </p><p>longer focal length camera lens is a great help (see Recommended Accessories). One of the biggest </p><p>challenges is getting accurate focus. The Moon may well appear to be in focus in a viewfinder, only </p><p>to appear as a blur when you see it on a computer. If you have terrestrial objects in the distance, you </p><p>can use these to tune your focus accurately. Otherwise, it is down to sharp eyes and luck. </p><p>Fig 11 The Moon at 55mm Focal Length </p></li><li><p>Phils Scribblings </p><p>P a g e | 12 </p><p>Fig 11 was taken using my older DSLR at 55mm focal length, as I did not have a longer focal length </p><p>lens at the time of capture. Although it shows the lunar seas quite clearly, the image is too small to </p><p>show craters. Interestingly, I took the photo in daylight from Aruba in the Caribbean. </p><p>Fig 12 Moon at 300mm Focal Length </p><p>Fig 12 is a much more recent effort and shows a lot more detail on the lunar surface. The crater </p><p>Tycho is clearly visible near the bottom and others are visible, too. Although it does not match my </p><p>efforts with telescopes, it shows the lunar phase (nearly but not quite full) and the major features. I </p><p>used ISO 400 and an exposure time of 1/2000 second. You should use a longer exposure time if the </p><p>Moon is low in the sky and/or partially covered by thin cloud. </p><p>The great thing about this method is that it allows you to record the lunar phases. I often use it when </p><p>I am short of time or am grabbing a shot through a gap in the clouds. I nearly always use a focal </p><p>length of 300mm and a brightness setting of ISO 400. I vary the exposure time from 1/200 to 1/4000 </p><p>second, depending on the lunar phase, the altitude of the Moon above the horizon and the presence </p><p>or absence of any cloud. Any slight over or under exposure can be dealt with using image processing </p><p>tools. </p><p>The Sun Frequent readers of Phils Scribblings and visitors to my website know of my fascination with our </p><p>nearest and dearest star. You should also be aware that there are safety risks in solar viewing. </p><p>Looking at the Sun through a viewfinder is dangerous, so PLEASE make sure that you use an </p><p>approved solar filter, best obtained from an astronomical supplier. Incorrect use of a camera for </p><p>solar photography can damage the camera as well as your eyes. Even with an appropriate solar filter, </p><p>the Sun is noticeably brighter than the Moon. I think it could be possible to capture sunspots at very </p></li><li><p>P a g e | 13 </p><p>ASTROPHOTOGRAPHY WITH A DSLR </p><p>short focal lengths but Ive never tried it. Ive only ever used a lens at 300mm focal length and never </p><p>used a brightness setting other than ISO 100 (the lowest). At the time of writing, it was near a s...</p></li></ul>


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