Introduction to DSLR Astrophotography
Gary Lintern www.garylinternphotography.com
Where Do I Start? The easy answer is that you begin with whatever DSLR equipment you already own. Photography is one of those hobbies, where people are constantly tempted to spent money on gear. Don't get me wrong, it helps, but expensive kit doesn't make you a good photographer. Practice and steady improvement does. Besides, if you invest in more equipment before you have the skills to use it, you'll almost certainly buy things you don't need. Even if you have an entry-level DSLR (such as the Nikon 3000-series or the Canon 1000-series) and a kit lens (18-55mm is most common), you can still photograph the night sky. The main advantages people with more expensive gear will have are:
greater flexibility in ISO settings, with less noise.
a better LiveView function (but not always!).
they might have lenses which can capture more light.
they might have lenses with a longer focal length (for more distant targets).
they may be able to capture better colours.
a more rugged camera body, that can withstand knocks and rain.
If you have a basic camera model, can you stand not having those . . . at least while you learn? There's only one factor which would make a camera upgrade more urgent, and that's if you're unable to shoot in RAW. The RAW format is very useful for all kinds of night photography, and will allow you much more flexibility in the edit. Apart from that, you might consider getting a more sturdy tripod, but you don't need to spend a fortune. Just bear in mind, if you can't stabilise your camera so it's rock solid, you won't be able to take good long exposure shots.
Optional Extras Consider buying an intervalometer (timer). Third party models can be purchased for as little as £10 on eBay. Not only will this work as a remote control (allowing you to shoot very long exposures in bulb mode), but you can also program it to take a predetermined number of shots, each for a specific duration. Some cameras have this built-in as a time lapse function. It's a standard feature in some Nikon DSLRs.
If you own a telescope, and want to have a go at connecting your DSLR to it, you'll need a t-ring. If your telescope only has a 1.25" fitting, you'll need a t-ring and an adaptor. This shouldn't cost too much, e.g. less than £10 for a ring, or less than £20 for a ring and adaptor. Buy metal ones if you can. They're usually much more sturdy than the plastic alternatives.
Settings and Lens Choice If you want to photograph stars, you'll be best off with a lens which has a wide aperture (low f-stop number). Also, unless you're photographing very distant targets, you'll get better results with a wide lens. I mostly use a Canon 24mm f/1.4 prime, which is a beautiful piece of glass. You don't need to go that far, though. However, if you can afford it, get a lens with a wide aperture (f/2.8 is perfect, but even f/4 should do a good job). Try lenses before you buy, if you can. You might consider renting an expensive lens for a weekend, and giving it a thorough test before parting with any money. Remember that some online and high street retailers allow you to buy and return items which don't meet your expectations. At the very least, take your camera body to a shop, and try some lenses there. If you want to save money, consider a manual lens because, if you're only intending to shoot at night, autofocus is pretty much redundant. So, for general star photography, go for a wide lens, and set it around the widest aperture (experiment to see what gets the best results). In terms of exposure length, you may have heard of the 'Rule of 600', which means you divide 600 by the focal length of the lens you're using, to get the maximum recommended exposure. If you've got a zoom lens, look at the figures on the lens body, to find the focal length you're using. So, for example, 600 / 24 = 25, meaning the 'Rule of 600' dictates that I can use a 25 second shutter speed with my 24mm lens. What happens if you expose for too long? The stars begin to visibly trail. Remember the big ball of rock you're standing on completely rotates once a day. So, relative to a vantage point on the Earth, the stars, moon, and planets are moving constantly. I'm not a fan of the 'Rule of 600'. In my experience, the resulting shutter speed is too long, and the stars streak. I've found that using 500 is better for crop-sensor cameras, and 400 works well for full-frame DSLRs. In my case, with a Canon 5D Mk3 and a 24mm lens, 400 / 24 = 16.67. I err on the side of caution, and never go over 15 seconds. It seems to get good results. Even though you've set your lens to a wide aperture, and are using a slow shutter speed, you'll find you camera still needs a bit of help to capture all that light. Find out how high you can get your ISO on a dark night, without the noise (grain on the image) becoming too noticeable. With an entry-
level DSLR, you might find you can comfortably work at ISO 400 or 800. With a more expensive camera, use ISO 3200 if you can. Deliberately overexposing is also known as 'exposing to the right'. You end up with a grey background, but can easily adjust for that later, with the RAW sliders in your editing software. It allows you to maximise the amount of light you can get from the stars. Focusing on stars can be tricky, but there are a few tried and tested methods. If the moon is up, you may find that you can autofocus on it, switch to manual, and then use that focus setting for the rest of the night, unless you knock your camera. If the moon isn't up, you're going to have to switch to manual focus and stay in it. If the LiveView on your camera is good, and you're using a wide aperture, you may find you can focus manually, using the screen on the back of your camera. This involves finding one or more bright stars, pointing the camera at them, and using the 5x and 10x maginification buttons to make them bigger. It's then just a matter of moving your focus ring until you reach maximum sharpness. It should then remain sharp for the rest of the night. Finally, if the first two methods don't work for you, you'll need to use trial and error. You start by tuning the focus ring all the way to 'infinity' (many lenses mark this with a
∞ symbol). On an aside,
you might think 'infinity' is the perfect setting for photographing stars. I'd be inclined to agree. Unfortunately, lens manufacturers allow for thermal expansion and contraction, and 'infinity' isn't really infinity. So, start at the far end of your lenses focus ring, and take a photograph of the stars. Check it on the screen of your camera, move the focus ring a bit, and then repeat until the stars are sharp. Once you're in the right ball park, fine tune it, using the same procedure . . . then try not to bump the focus ring for the rest of the night! Some people go as far as marking the lens with a scratch or some liquid paper. A less destructive alternative would be to lock it in place with gaffer tape. If you want to photograph more distant objects (or the moon), you're going to need a much longer lens. Even 300mm will only fill part of the frame with the moon. However, you can get perfectly nice shots of some deep sky objects, such as the Orion nebula, with a 200mm lens (although longer is better). There's more information later on about how to find and capture deep sky objects. Remember, the above rules still apply for maximum shutter speed. So, using a 200mm prime on a full-frame camera, gives you a maximum of 2 seconds (400 / 200), before stars begin to streak. With
a lens that long, that shutter speed is probably too generous. You may find you only have one second. Also, bear in mind that until you're more familiar with the night sky, targets are harder to find with a long lens, due to you only having a limited field of view. There is some good news, though. Once you've practised until you exhaust the possibilities of your current equipment, you might want to consider investing in a tracking mount, such as an Astrotrac.
They're not cheap, but when you mount your camera on an Astrotrac, and set it up carefully, you have as long as two hours to photograph whatever you want, without streaks. This is because a tracking mount rotates your camera slowly, in order to keep up with the rotation of the Earth. They're not for beginners, though, and are therefore beyond the scope of this manual. If you decide to buy a tracking mount, call a telescope shop, and ask their advice on current models.
The Moon Conditions for night photography are different every night of the month, due to both the weather and the cycle of the moon. Get to know the moon cycles, because they're very important. There are plenty of apps for this, or you could visit a site such as www.timeanddate.com. Once you've inputted your location, and the date you're interested in, you'll see something like this:
Obviously, you're going to get the most complete shot of the moon when it's full. However, the surface of the full moon is illuminated with direct sunlight, so you won't be able to see the craters very well, because there won't be many shadows. The full moon is also a poor choice for photographing stars, because it's so bright. Remember the light from the moon is sunlight. Of course, the light from the stars is too, only they're much more distant suns. If you want shots of the craters and 'seas' on the moon, aim for a few days either side of the First or Third Quarter, so you get some nice shadows.
There are affordable lens solutions, if you're interested in close-ups of the moon. I use an Opteka 1300mm lens, with a doubler. At its longest focal length, the moon is actually bigger than the frame size!
They're not for everyone, and please don't take this as a recommendation. But for less than ÂŁ200 new, it's a relatively cheap solution to enable you to get shots like this:
If you're using a tripod with an Opteka, you'll need to mount the lens on it, and allow the camera to hang off the end. I've found it's much easier not to use a tripod. I rest mine (on a beanbag for protection) on a solid object such as a car, a wall, a tree, or the attic window. Please be aware that with a lens that long, the difference between focused and blurred is miniscule. It can also take a while to find the moon, because of the narrow field of view. Regarding camera settings, you need a fast shutter speed because, remember, you're photographing sunlight. Depending on the available light and cycle of the moon, you'll probably find the ideal setting is somewhere between 1/200th and 1/1000th of a second. The good news is, because you're using such a fast shutter speed, you can often get away with handheld shots.
You may as well set your camera to shutter priority when photographing the moon, as the shutter speed is the most important variable. As long as you're in focus, the aperture doesn't really matter. ISO is down to personal preference, but I usually work at 400 or 800 to minimise noise. Going back to the moon cycles for a moment, they're just as important if you want to photograph stars or deep sky objects. You'll also find more detailed charts on www.timeanddate.com with daily rising and setting times of the moon:
'Moonrise' and 'Moonset' speak for themselves. The 'Meridian' part of the table shows you the time at which the moon will be at its highest. It also gives the distance from the Earth and illumination levels (as a percentage). If you compare Meridian figures across the year, you'll find the moon rises highest in the winter, and lowest in the summer - the opposite of the sun's annual pattern. Note that for several consecutive nights (January 3rd to 9th, in this example) there is no moon between sunset and midnight. Those are the best nights to observe and photograph the stars (weather-permitting). But, even the next few days would be okay, because even when the moon is up, it'll only be a sliver of light.
Planning Shoots There's a fantastic piece of freeware, called Stellarium, which allows you to work out where your intended targets will be, on a specific day and time. It's also very handy for exploring the night sky at home, and learning the constellations. You can download Stellarium at: www.stellarium.org It's available for the PC and Mac, and they also offer a mobile app. The opening screen (depending on the time of day) will look something like this:
Note the points of the compass in red, on the horizon. This view is to the south (red S). There are three menus in Stellarium, one of which is permanently visible in the upper right. The other two pop up when you move the mouse pointer to the left side of the foot of the screen, or the bottom of the left side of the screen. One function you need to know on the bottom menu is the button for closing the program. In this screen shot, it has a red ring around it.
Another useful function on the bottom menu is the button which toggles between normal and night view (red, to protect your night vision).
If you go over to the menu on the left of the screen, you'll see a few more buttons. The top one activates the Location Menu. Here' you'll be able to enter the nearest city, so the software knows (roughly), the longitude and latitude you want to view from.
The next button down is the Date/Time Window. It will enable you to select any date or time you wish, and will display the sky as it will be (or was) then.
After changing the time from 13.54 to 20.54, the sky darkens and the stars and planets appear.
The third button down is for the Sky and Viewing Options Window.
If you're interested in finding the Milky Way, adjust the brightness from 1 to 5, and it becomes easier to see (to the left of the window).
You can zoom in and out with either the mouse wheel, or the Page Up & Page Down keys. It's possible to zoom out completely, so you see the entire sky as a circle.
In the same menu, you can click the Markings submenu to add labels, art, and boundaries to the constellations.
The easiest way to navigate the sky is to click your mouse button, and move the mouse. Here, I've centred it on Orion.
Zooming in a bit, the Orion Nebula becomes visible, around the middle star of three that form the sword. A 200mm lens, or longer, will be enough to get a glimpse of the nebula, and should allow you to see some of the blues, reds, and purples - even with a one second exposure.
I've now moved up and to the right a bit, into Taurus. There's a cluster of stars, visible to the naked eye, called the Pleiades or Seven Sisters.
Zooming into the Pleiades, you'll see they have a blue tint. Stars are different colours (reds, yellows, blues, and various shades in between - and white, of course). We just see them all as white, because our night vision isn't very good at colour perception. They'll show up on your camera though.
Finally, we move across the sky to Andromeda. You'll be able to find this constellation easily if you can locate Cassiopeia, which looks like a big letter 'W' in the Milky Way. Between Cassiopeia and Andromeda is a blurry patch, also visible to the naked eye. This is the Andromeda Galaxy. It's much the same shape as the Milky Way, our own galaxy. To us, though, the Milky Way appears as a band of stars surrounded by gas clouds, because we're inside, looking out.
It's also possible to get a decent shot of the Andromeda Galaxy with a 200mm (or longer) lens. However, all three of these deep sky objects I've shown you here, will look better with a long exposure, but you'd need a tracking mount to do that. Alternatively, you can stack lots of short exposures together, but that's another lesson for another time!
Editing As this isn't a manual for Photoshop or Lightroom, and people use a variety of other programs, I'll leave out the specifics of editing images of the night sky. You'll find that, as long as you shoot in RAW, you can take care of most issues with the RAW sliders. If you end up with an unwanted vignette after adjusting the RAW settings, use the Vignette Removal tool in your software to reduce it, as much as possible, without compromising the rest of the image. It can be a fine balancing act. Make a slight crop, if you need to. Apart from that, experiment with Brightness and Contrast (including Levels and Curves), and with adjusting the Vibrance and Saturation of specific colours. This can be particularly useful for reducing the impact of light pollution on the horizon. Consider using the Dodge and Burn tools to manually enhance the light and shade in your image. Don't overdo it though. Subtlety is key. You'll probably find your image will benefit from a little bit of noise removal, but again, don't overdo it or you'll end up with colour bands. Finally, if you have a degree of proficiency with using Layers and Blend Modes, you might want to temporarily remove the stars so you can edit other parts of the image. One way to achieve this is to use a 'Remove Dust and Scratches' filter, and then blend them back in when you're done.
Seeing in the Dark Humans have two visual systems, corresponding to two distinct types of cells in our eyes. During the day, we tend to mostly use the centres of our eyes, in order to see in colour and focus on detail. At night, colours seem more muted but we become more aware of light and shade, and movement. You've probably noticed that if you're in a dark room, it's hard to see anything at first. However, in time, your vision adapts. In most people, this takes around 30 to 45 minutes. Unfortunately, it can undone very quickly if you use a torch, or catch the glare of a car's headlights. Not only will this make it harder for you to navigate around your environment, but it will also reduce the brightness and amount of stars you're able to see. Fortunately, there's a solution. By and large, our night vision is immune to red light. One answer is use a red torch such as the Skywatcher Dual LED Flashlight. Plenty of alternatives are available. Just search for 'red astronomy torch'.
If you intend to light paint part of the landscape you're photographing, you'll either need to invest in some red goggles or glasses, or just accept your night vision is going to be far from optimal. For illuminating landscapes, you need a white LED torch, ideally one with a focusable beam to improve accuracy and power. LED Lenser torches are excellent. The P14 or the smaller and slightly cheaper P7 are both good multipurpose torches.
Useful Links
International Dark Sky Association: http://darksky.org
Dark Sky Discovery Sites (UK): http://www.darkskydiscovery.org.uk
The Federation of Astronomical Societies (UK): http://fedastro.org.uk
List of Astronomy Societies (UK): http://www.awesomeastronomy.com/astronomy-resources/astronomy-societies
The 'Cloudy Nights' Forum: http://www.cloudynights.com
The UK Astro Imaging Forum: http://ukastroimaging.co.uk/forums