{"id":19328,"date":"2021-06-23T11:21:11","date_gmt":"2021-06-23T11:21:11","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=32388"},"modified":"2021-06-21T14:05:10","modified_gmt":"2021-06-21T14:05:10","slug":"deep-sky-astrophotography-a-beginners-guide","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/deep-sky-astrophotography-a-beginners-guide\/","title":{"rendered":"Deep-sky astrophotography: a beginner\u2019s guide"},"content":{"rendered":"

\"The <\/p>\n

There are many branches of astrophotography to explore, from capturing the Moon\u2019s craters, to wide-field starscapes of our Milky Way. But perhaps the most demanding images to take are those of deep-sky objects.<\/p>\n

Deep-sky photography includes images of nebulae<\/a>, galaxies<\/a> and star clusters<\/a>, and whether you\u2019re a seasoned daytime photographer or a complete beginner, doing justice to these faint fuzzy objects takes time and patience.<\/p>\n

However, practice makes perfect and deep-sky photography is extremely rewarding right from the word go: you can image a target and unlock details that are simply invisible to visual astronomers.<\/p>\n

For more help, read our astrophotography guides<\/a>.<\/strong><\/em><\/p>\n

\"Whirlpool<\/div>\n
<\/i> Whirlpool Galaxy<\/a> by Steve Porter, Bardsey Island, North Wales, UK. Equipment: Meade 10\u2033 LX 200 ACF, EOS 6.<\/span><\/figcaption><\/span><\/div>\n

With a bit of practice, amateur astrophotographers can capture images of the deep sky reminiscent of the Hubble Space Telescope<\/a>.<\/p>\n

If you\u2019re curious about deep-sky imaging and want to know what equipment you need (versus what you may want to buy later once you\u2019ve honed your skills) and what techniques you\u2019ll need, below we\u2019ll run through some key elements that will have you photographing galaxies and nebulae in no time.<\/p>\n

Deep-sky photography equipment<\/strong><\/h1>\n

Deep-sky imaging makes great demands on your kit because you need to achieve long exposures to capture the maximum amount of detail in your images. The good news is there are many setup options for beginners.<\/p>\n

The type of camera you use is particularly important, but there are other things to consider, so we\u2019ll also look at telescopes and then move on to astronomy accessories including telescope mounts<\/a>, autoguiding systems and filters<\/a>.<\/span><\/p>\n

Cameras<\/strong><\/h2>\n
\"How<\/div>\n
<\/i> Deep-sky beginners may want to get started with a DSLR camera. Credit: Gajus \/ iStock \/ Getty Images Plus<\/span><\/figcaption><\/span><\/div>\n

You can start deep-sky imaging with a DSLR camera. This meets the basic needs, as most have a Bulb mode to run long exposures, adjustable light sensitivity (ISO) and are relatively easy to operate.<\/p>\n

But perhaps a DSLR\u2019s great advantage for a beginner is that it\u2019s a relatively uncomplicated setup. Indeed, there are some deep-sky objects you can image using a DSLR and a zoom lens, such as the Orion Nebula and the Heart and Soul Nebulae.<\/p>\n

For more info, read our tutorial on how to use a DSLR camera<\/a> or our guide to the best astrophotography cameras<\/a>.<\/p>\n

You need a sturdy mount (which we\u2019ll discuss below), plus a remote shutter release such as an intervalometer. This will allow you to set the number of exposures to be captured and the exposure length, and it will also give you the means to start an imaging run without touching the DSLR.<\/p>\n

\"A<\/div>\n
<\/i> A remote shutter release helps
to capture images of the deep sky, as you can start an imaging run without touching the camera. Credit: Pete Lawrence<\/span><\/figcaption><\/span><\/div>\n

DSLRs can capture impressive deep-sky images, but the sensors don\u2019t perform well on exposures over 5 minutes For longer exposure times, CMOS and CCD cameras offer lower noise (unwanted artefacts).<\/p>\n

CMOS and CCD cameras<\/a> are similar to operate. These are dedicated astrophotography cameras, and don\u2019t look like a point-and-shoot camera \u2013 they\u2019re more like specially adapted industrial cameras.<\/p>\n

They come in either colour or monochrome versions (the latter requires the purchase of colour filters). What sets them apart from a DSLR is the sensor.<\/p>\n

\"QHYCCD<\/div>\n
<\/i> QHYCCD QHY 168C CMOS colour camera. Credit: BBC Sky at Night Magazine<\/span><\/figcaption><\/span><\/div>\n

The CCD performs better at longer exposures than the CMOS, so to gain the best results expect to run a CCD with exposure times between 10 and 20 minutes.<\/p>\n

CMOS and CCD deep-sky cameras are \u2018passive-cooled\u2019 or \u2018active-cooled\u2019, which helps to reduce noise.<\/p>\n

Passive cooling uses fans to prevent the sensor from overheating and introducing noise, while active cooling combines fans and a Peltier system to maintain a fixed temperature.<\/p>\n

A CMOS- or CCD-based setup is more complicated than a DSLR because you need a laptop and software to control the camera and see the images it\u2019s taking, which also means access to mains power or a healthy battery is required.<\/p>\n

As we\u2019ll discuss, these cameras also bring with them the need for other accessories such as autoguiding systems.<\/p>\n

For more on CMOS, read our CMOS astrophotography<\/a> guide.<\/strong><\/em><\/p>\n

Telescopes<\/strong><\/h2>\n
\"Celestron<\/div>\n
<\/i> Celestron StarSense Explorer LT 70AZ refractor<\/span><\/figcaption><\/span><\/div>\n

When you image the deep sky with a telescope, it takes the place of a large lens for your camera. But, unlike visual astronomy, the telescope aperture won\u2019t limit detail \u2013 the camera allows us to capture small features even with a small telescope.<\/p>\n

However, a telescope\u2019s focal length versus its aperture is key as this determines the focal ratio, or f\/ number (for more on this, read our guide to telescope stats<\/a>).\u00a0The smaller the f\/ number, the greater the telescope\u2019s light-gathering capability.<\/p>\n

All telescopes types can be used for astrophotography, but Cassegrains are best kept for photographing the planets<\/a>.<\/p>\n

\"Large<\/div>\n
<\/i> Large Schmidt-Cassegrains are a popular choice for capturing the planets. Credit: BBC Sky at Night Magazine<\/span><\/figcaption><\/span><\/div>\n

Reflectors and refractors are the preferred choices on the deep sky. Refractors offer the best optics in a small and light body, but are generally more expensive.<\/p>\n

Reflectors come in cheaper, but at the cost of size and weight. Some reflectors also have focusing issues once a camera
\nis attached, which require the mirror position to be adjusted.<\/p>\n

Field curvature can be an issue with both types of telescope, but this is easily corrected with a field-flattener<\/a>.<\/p>\n

Flatteners are one of the more expensive accessories and require precise positioning to work at their best.<\/p>\n

For those intending to invest in a telescope and CCD camera, the Astronomy Tools CCD Suitability Calculator<\/a>\u00a0helps to determine how two models will perform together. This takes the focal length of the scope and combines it with the pixel size of the CCD to assess its potential for deep-sky imaging.<\/p>\n

You can also use our Astronomy Field of View Calculator<\/a> to help.<\/p>\n

Browse all of our telescope reviews<\/a>.<\/strong><\/em><\/p>\n

Getting set up for deep-sky photography<\/strong><\/h1>\n
\"Fitting<\/div>\n
<\/i> Fitting a guiding system to your setup isn\u2019t crucial for beginners, but a sturdy mount is. Credit: Pete Lawrence<\/span><\/figcaption><\/span><\/div>\n

The first thing to ensure for deep-sky imaging equipment is that you have a sturdy mount. For astrophotography<\/a> this is an essential bit of kit because the maximum exposure length depends on it, and it will protect your imaging equipment and help locate your target if it\u2019s a Go-To mount.<\/p>\n

For deep-sky imaging you need an equatorial mount (rather than an altaz mount), in addition to motorised axes (or the declination axis at a minimum) that will allow it to \u2018track\u2019 the apparent movement of the night sky, which is known as \u2018sidereal tracking\u2019.<\/p>\n

\"Aligned<\/div>\n
<\/i> Aligned on the north celestial pole, an equatorial mount makes it easy to track stars as they move from east to west through the night.<\/span><\/figcaption><\/span><\/div>\n

Tracking accuracy is paramount as this is what creates pin-sharp stars. While this is largely due to how well the mount is polar aligned, it\u2019s also down to the motor\u2019s efficiency.<\/p>\n

The mount\u2019s payload is important too, because this can also affect tracking. You will find that imaging payload requirements are different from visual ones because astro imaging requires more precision to stay on target.<\/p>\n

The payload listed in the mount\u2019s specifications is typically for visual purposes; halve that figure for imaging.<\/p>\n

Guiding<\/strong><\/h2>\n

As beginner deep-sky imagers develop their skill and confidence, many opt to add guiding software to their setups.<\/p>\n

This connects with the mount to make tracking corrections: a guide camera replaces the finderscope and focuses on multiple \u2018guide stars\u2019 as reference points.<\/p>\n

This information, fed through the guiding software on a laptop, ensures the mount stays <\/span>on target and allows for increased exposure times.<\/p>\n

Guiding makes a radical difference to images because:<\/p>\n

    \n
  1. The increased image exposure times enhance detail<\/li>\n
  2. Most guiding software has a dithering function<\/li>\n<\/ol>\n

    Image dithering reduces \u2018walking noise\u2019, which is an unwanted artefact that comes from stacking image files.<\/p>\n

    But when you\u2019re starting out, one thing to remember is that guiding can complicate things \u2013 it\u2019s not an essential step for beginners, and it can be worth parking until you\u2019re more confident with the camera and mount.<\/p>\n

    Focal reducers & filters<\/strong><\/h2>\n
    \"A<\/div>\n
    <\/i> Telescope filters. Credit: Pete Lawrence<\/span><\/figcaption><\/span><\/div>\n

    Depending on the telescope\u2019s focal length, focal reducers can come in handy. These reduce the focal length of your telescope by a factor of between 0.5 and 0.8, depending on the model.<\/p>\n

    This allows those with long focal-length telescopes to access more deep-sky targets, as it creates a wider field of view.<\/p>\n

    Deep-sky astrophotographers also end up investing in narrowband or light pollution<\/a> filters.<\/span><\/p>\n

    Light pollution filters prevent artificial light from reaching the camera sensor, while narrowband filters capture wavelengths emitted from nebulae \u2013 including Hydrogen-alpha (Ha), Oxygen (OIII) and Sulphur (SII) \u2013 and cut out most <\/span>other electromagnetic waves.<\/p>\n

    \"NGC<\/div>\n
    <\/i> NGC 281 by Gary Opitz, Rochester, NY, USA. Equipment: TEC140APO refractor, ZWO ASI1600MM camera, ZWO Ha 7 nm filter, Astrodon OIII 5 nm filter, Orion Atlas mount<\/span><\/figcaption><\/span><\/div>\n

    Narrowband filters enhance contrast and details in a deep-sky image. These filters are available for most types of camera \u2013 not just CCDs.<\/p>\n

    Two-inch filters can be installed between the telescope eyepiece barrel and camera adaptor, plus there are also clip-in options for DSLRs.<\/p>\n

    Some astro imagers also use a filter wheel if they are using several filters in one night. These are designed to make the transition from one filter to another easier <\/span>and it means you don\u2019t have to detach the camera.<\/p>\n

    Deep-sky image processing<\/strong><\/h1>\n
    \"How<\/div>\n
    <\/i> Image processing is a key component of astrophotography. Credit: Farknot_Architect \/ iStock \/ Getty Images<\/span><\/figcaption><\/span><\/div>\n

    Those new to astrophotography may think that a processed deep-sky image is artificial or \u2018faked\u2019, because it looks so different to the image of the same object on the back of the camera.<\/p>\n

    However, the image processing<\/a> stage is arguably as important as the capture stage \u2013 it is how you draw out the detail that cannot be seen.<\/p>\n

    As deep-sky objects are shot in RAW<\/a> format, no colour corrections, exposure compensation <\/span>or noise reduction is done in the camera \u2013 it\u2019s all done at the processing stage.<\/p>\n

    Instead of seeing processing as \u2018faking\u2019 a deep-sky image, it\u2019s better to see it as unlocking the data suppressed in the RAW files.<\/p>\n

    Processing a deep-sky object involves three main stages:<\/p>\n

      \n
    1. Image registration<\/li>\n
    2. Image stacking<\/a><\/li>\n
    3. Final image process<\/span><\/li>\n<\/ol>\n

      All\u00a0 of these are done using image-editing software. DeepSkyStacker<\/a> and Sequator are used for registering and stacking RAW deep-sky images, while Photoshop, <\/span>GIMP and PixInsight<\/a> are used for the final stage.<\/p>\n

      Calibration frames<\/strong><\/h2>\n
      \"A<\/div>\n
      <\/i> A RAW frame (left) straight from the camera and a final processed image (right) of the Elephant\u2019s Trunk Nebula, show how crucial processing is to unlocking the data held in deep sky captures<\/span><\/figcaption><\/span><\/div>\n

      Also important are the \u2018calibration frames\u2019 that are added during the stacking process.<\/p>\n

      Learning to take good calibration frames will make a difference to your final image. They will reduce unwanted noise, vignetting (reduction in image brightness at the edges <\/span>of the field of view) and sensor artefacts like motes of dust and dead pixels from a stack of images, which then allows for more scope when processing.<\/p>\n

      The three main types of calibration frame are dark frames<\/a>, flat frames<\/a> and bias frames. Darks and biases reduce electronic and sensor noise, while flats reduce vignetting<\/a>.<\/p>\n

      Both DSS and Sequator have sections to add these files. It\u2019s simple to take both types.<\/p>\n

      \"A<\/div>\n
      <\/i> A stacked master dark frame. Credit: Steve Richards<\/span><\/figcaption><\/span><\/div>\n

      Dark frames are taken at the same ambient temperature, exposure and ISO as your image <\/span>frames.<\/p>\n

      To get them, pop your lens cap on at the start or end of your imaging run and fire off up to 30 exposures.<\/p>\n

      Bias frames don\u2019t require a lens on the camera, but they need the same ISO as your image frames. <\/span>Keep the camera cap on a DSLR, set the exposure to the fastest exposure time and fire off the bias frames. <\/span><\/p>\n

      Flat frames need to be taken at the same ISO, aperture and focal point as the image frames \u2013 so don\u2019t nudge the scope or lens after your imaging session.<\/p>\n

      You\u2019ll need a white screen \u2013 such as a blank piece of A4 \u2013 that covers your scope or lens\u2019s field of view. The exposure time for a flat file varies depending <\/span>on if you\u2019re using a DSLR, CMOS or CCD camera.<\/p>\n

      The two contrasting images of the Elephant\u2019s Trunk Nebula<\/a> above show why processing is so important. By stacking, adding calibration frames and using processing software the initial RAW camera image is transformed into a celestial marvel.<\/span><\/p>\n

      How to photograph a galaxy<\/strong><\/h1>\n
      \"The<\/div>\n
      <\/i> The Andromeda Galaxy. Credit: Charles Thody<\/span><\/figcaption><\/span><\/div>\n

      The Andromeda Galaxy, M31, is a great beginner\u2019s deep-sky object target because it\u2019s easy to find and can be imaged with a DSLR and lens.<\/p>\n

      The equipment needed to capture an image like this comprises a DSLR, a Go-To tracking mount and an intervalometer.<\/p>\n

      Regardless of the target, every deep-sky imaging session should start with polar aligning<\/a>. By finding Polaris and positioning it in your mount\u2019s polarscope, you calibrate the mount so that it can track the stars accurately.<\/p>\n

      You should then perform a three-star alignment with the mount \u2013 this helps its Go-To function find targets reliably.<\/p>\n

      It also possible to safely polar align during the day<\/a>.<\/p>\n

      Whether imaging galaxies or nebulae, achieving sharp focus is crucial. With either target it\u2019s the same method: focus on a bright star, such as Vega (Alpha (\u03b1<\/span>) Lyrae), before finding your target.<\/p>\n

      \"Use<\/div>\n
      <\/i> Vega can be found in the Lyra constellation. Credit: Bernhard Hubl \/ CCDGuide.com<\/span><\/figcaption><\/span><\/div>\n

      After locating the galaxy, try out d<\/span>ifferent ISO levels and exposures. As the Andromeda Galaxy has a bright galactic core, select an exposure time that doesn\u2019t \u2018blow out\u2019 the centre of your image.<\/p>\n

      If the core is overexposed, you\u2019ll lose detail from the inner dust lanes when it comes to processing the image. Try 90 minutes <\/span>of 1-minute exposures at ISO 800.<\/p>\n

      You can combine shorter and longer exposures, however, and his can be done <\/span>via the stacking process in Photoshop or DeepSkyStacker.<\/p>\n

      In DSS, you can separate different exposure lengths into <\/span>\u2018groups\u2019 and stack them. In Photoshop, you stack the frames for each exposure separately to end up with a TIFF file for each.<\/p>\n

      After processing the TIFFs separately, you layer one image on top of the other and blend with the \u2018Hide All\u2019 and \u2018Reveal All\u2019 masks.<\/p>\n

      For more info, read our guide on how to photograph the Andromeda Galaxy<\/a>.<\/strong><\/em><\/p>\n

      How to photograph a nebula<\/strong><\/h1>\n
      \"The<\/div>\n
      <\/i> The North America Nebula, taken with a Canon 700D DSLR \u2013 using 2 hours of 4\u2019 exposures per filter (Ha and OIII). Credit: Charlotte Daniels<\/span><\/figcaption><\/span><\/div>\n

      The North America Nebula is another big, bright deep-sky object that\u2019s ideal for deep-sky astrophotography beginners.<\/p>\n

      A part of it, known as the Cygnus Wall (see above), shows up even in 10-20 second exposures with a high ISO setting, helping you know when you\u2019ve found the target and how to position it for the rest of the imaging run.<\/p>\n

      To capture the image above, we used a modified DSLR with a clip-in Hydrogen-alpha (Ha) and Oxygen (OIII) narrowband filter added for more detail.<\/span><\/p>\n

      I<\/span>f you\u2019re shooting this object with an unmodified DSLR, the final image would <\/span>look mostly red, because the camera would not be sensitive to subtle OIII emissions from the nebulae.<\/p>\n

      Instead, it would just capture some of the Hydrogen. The OIII data we\u2019ve gathered from the filter is blue in our final image above.<\/span><\/p>\n

      \"North<\/div>\n
      <\/i> North America and Pelican Nebulae, by Neil Wyatt, Branston, Staffordshire, 20 and 21 July 2020. Equipment: ZWO ASI 1600MM Pro mono camera, Sky-Watcher 130PDS Newtonian, Sky-Watcher HEQ5 Pro mount<\/span><\/figcaption><\/span><\/div>\n

      We also used guiding for this astrophoto, which allowed us to run four-minute exposures. Without guiding, we would have been limited to about two minutes before the mount started to drift and blur the detail.<\/p>\n

      In the end, we shot a total of two hours of Ha and two hours of OIII for the final image.<\/p>\n

      The way we processed the North America Nebula image was different to Andromeda, because of the narrowband filters.<\/p>\n

      We stacked and processed each filter separately in DSS, and set the resulting TIFF files to monochrome in Photoshop.<\/p>\n

      We then performed a histogram stretch on each to get as much detail as possible, before combining our Ha data with the Red colour channel and the OIII data with the Blue colour channel.<\/p>\n

      The Green channel was then set to 50% Ha and 50% OIII. The result is this colour image that benefits from all the extra details our narrowband filters have captured.<\/p>\n

      For another nebula challenge, read our guide on how to photograph the Orion Nebula<\/a>.<\/strong><\/em><\/p>\n

      Have you captured a beautiful deep-sky image? We\u2019d love to see it. Be sure to send us your images or share them with us via Facebook, Twitter and Instagram.<\/strong><\/em><\/p>\n

      Charlotte Daniels is an amateur astronomer, astrophotographer and space journalist.<\/em><\/strong><\/p>\n

      This guide originally appeared in the July 2021 issue of <\/em>BBC Sky at Night Magazine.<\/em><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

      There are many branches of astrophotography to explore, from capturing the Moon\u2019s craters, to wide-field starscapes of our Milky Way. But perhaps the most demanding images to take are those of deep-sky objects. Deep-sky photography includes images of nebulae, galaxies and star clusters, and whether you\u2019re a seasoned daytime photographer or a complete beginner, doing […]<\/p>\n","protected":false},"author":24,"featured_media":0,"template":"","categories":[34],"acf":{"readingTimeMinutes":"15"},"uagb_featured_image_src":{"full":false,"thumbnail":false,"medium":false,"medium_large":false,"large":false,"1536x1536":false,"2048x2048":false},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"There are many branches of astrophotography to explore, from capturing the Moon\u2019s craters, to wide-field starscapes of our Milky Way. But perhaps the most demanding images to take are those of deep-sky objects. Deep-sky photography includes images of nebulae, galaxies and star clusters, and whether you\u2019re a seasoned daytime photographer or a complete beginner, doing…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/19328"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=19328"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=19328"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}