Are you ready for an Intro to Astrophotography?! Summer is a fabulous time to capture the night sky. The nights are warmer and more often clear and it’s Milky Way season. My aim is to give you an intro to astrophotography and a general understanding of what is a somewhat technical area. I hope is to teach you enough that you feel confident to give it a go.
I am a scientist and I have always been fascinated by the world around me. Being able to capture the night sky thrills both the scientist and photographer in me. It’s not easy, but with a bit of research and some luck, you too will be able to have a great feeling of achievement from astrophotography.
I would suggest that first and foremost you need a plan! There are a few more requirements with night photography and you want to set yourself up for success. If you can scout the location during the day, then this will really help make the most out of your night shoots.
Intro to Astrophotography ~ What you’ll need:
As for gear, you need a camera capable of full manual mode and a fast wide-angle prime lens. You can use a zoom lens but they tend to have narrower maximum apertures which can affect their light gathering abilities. I mostly use my Sigma Art 35 mm f/1.4. Ideally, I would use something with a shorter focal length, but the maximum aperture of f/1.4 is fantastic. You also need a tripod (I have a Manfrotto BeFree Advanced Carbon, but any lightweight one will do) and a flashlight or head torch to see where you are going. You might want to also invest in a head torch with a red light at some point because red light doesn’t blind your night vision.
For star trails you need an interval timer. I have a Canon 5D Mark IV and it comes with one inbuilt. Alternatively, you can cheaply purchase an external one. I also recommend a battery-operated lens warmer to keep condensation off but it’s not necessary and only really needed for taking long exposures particularly during cold nights.
Always shoot in RAW since it gives you the most flexibility in post-processing. Remember to charge your battery and I recommend having a completely empty SD card, especially if you plan on doing long exposures, as well as a few spare cards. I use 128 MB SD cards. I have two card slots and I simultaneously write to both of them. If one of the cards gets corrupted, then I have a backup. Finally, charge your mobile phone, pack any provisions you might need and tell someone where you are going and when to expect you back. Please keep safe!
Intro to Astrophotography ~ What to Capture:
A good starting point is to think about what you would like to capture. There are several possibilities but for this article I will focus on how to capture two things: the Milky Way and long exposure star trails. In both cases you need a clear, dark night-time sky. Light pollution will quickly drown out any signals from distant stars, especially when trying to capture the Milky Way.
There are a few different websites to find dark sky sites such as Dark Site Finder. If you can’t find a completely dark sky near to you then you can still try star trails, but remember to point your camera away from any direct light sources (cities, streetlights, etc.).
Also, important to note is the phase of the moon. Ideally, you want a new moon or as little moon as possible, especially for capturing the Milky Way. If the moon is in the wrong phase, not all is necessarily lost. Check the moon rise and set times because you may be able to plan your photographs for after the moon sets or before it rises.
For planning this I highly recommend an app called PhotoPills. It will tell you the phase of the moon, rising and setting times and it provides the same information for the Milky Way itself for your given location. You can also use its calendar feature to plan the best nights.
When we talk about photographing the Milky Way, we generally mean capturing the galactic core, which is the most densely packed and brightest part. This segment is visible above the horizon from roughly March to October in the Northern Hemisphere, and from February to October in the Southern Hemisphere. It has a rise and set time just like the sun and the moon. Early in the season it can be seen arching across the sky, but it becomes more of a vertical line as the season comes to an end.
Once you find your dark sky site, it is then time to think of interesting compositions. Look out for reflections in bodies of water and interesting foregrounds such as old buildings, hay bales, rocks and even just a lone tree. Once outside, I use another app called Stellarium to locate the Milky Way. There are several free alternatives.
Focusing on stars is tricky to say the least. Be patient and stick with it. They are very faint so you must use manual focus. I use my camera’s live view and I try to find a nearby bright object in the sky. For example, last summer Jupiter and Saturn were both near the Milky Way and very bright, so I used live view to manually focus on them. A trick is to increase the ISO which enables you to see the sky more brightly. Some cameras’ live view will let you zoom in as well. Alternatively, you could find the hyperfocal distance, but you need a strong light to illuminate a source far in the distance to be able to focus on it.
After selecting your composition and finding focus, the next step is to set your exposure. You will be pushing your camera to its limits, so it really pays to know it well. Finding the correct ISO to use is one of the key determining factors of success. Some cameras are ISO-invariant (for example several Fujis) while others are highly ISO-variant (several Canons) and perform better at certain ISOs. For digital cameras ISO creates an amplification of signal. This can be done in two ways, digitally or electronically.
Digital amplification can introduce noise, whereas electronic amplification can reduce noise. I always struggled with grain when using ISO 800 while others were using extremely high ISOs with little noise. Through researching astrophotography, I found out that my camera gets an extra ‘power boost’ from electronic amplification at higher ISOs, resulting in less noise. So higher really is better in my case. You can do a test and find your optimum ISO or refer to this chart which lists most manufacturers and models.
After you select your make and model, have a look at the graph. You want to stay to the left of any triangles, which indicates digital amplification and is more likely to result in noise. Some cameras will show a nearly flat line. This means that your camera is ISO-invariant. For others it will curve downwards. If this is the case, look for where the curve starts to flatten to find the optimal ISO. For my Canon 5D Mark IV this point is between ISO 1200 and 1600. For a lengthy discussion on this topic visit Petapixel.com.
The next important parameter is time. If you expose for longer than about 20 seconds you will get nascent star trails instead of pinpoint spot stars. For the Milky Way you want to capture spot stars, not streaky star trails. There is formula called the 500 rule which gives you the optimum exposure based on the crop-factor of your camera and focal length. It is:
However, this rule is somewhat outdated and does not factor in aperture. You can find a few different equations on the web such as the NPF rule, but the 500 rule is a good place to start. You can then check your histogram and adjust your settings accordingly.
As for aperture, you want to maximize the amount of light reaching the sensor while maintaining sharp focus. Again, you might want to test out what number this is for your lens, but as a general rule two to three f/stops down from the widest aperture is typically the sharpest. With that said, you may need to go wide open in order to not go above an ISO that introduces too much noise.
I usually leave my white balance in auto mode, and I generally get accurate star colours but if you want to set it manually then 3000 – 5200 K is a good starting place. This is dependent on how much light pollution is around. You can, for the most part, correct white balance in post-processing, assuming that the stars weren’t overexposed and that you shot in RAW.
One thing that you absolutely need to avoid is camera shake. Pressing the shutter button can cause this so you either need to use a remote trigger or set a delay on your camera. I use a two second in-built delay timer. Also turn off image stabilization and long exposure noise reduction. Image stabilization is not needed when using a tripod and noise reduction will greatly slow down your camera. Also remove any filters on your camera, especially UV filters because they will cause glare at night.
Lastly, one way of reducing noise in your final image is to take 5 – 10 images and ‘stack’ them in post-processing either using Photoshop or a dedicated program. You use these multiple images to ‘average out’ the noise. There are several tutorials on the web for how to go about this and which also cover processing your final images in general.
If you are outside of Milky Way season or just want to capture something different then a time lapse photo of the night sky can be very interesting. It is also more tolerant of light sources, either from light pollution or the moon. The general rule is that if you can see stars, then you can capture star trails. The downside is that it can be a lengthy process.
Again, for a good composition, look out for interesting foregrounds and reflections. The North Star or Polaris will remain relatively stationary with nearby stars circling around it. You can use the app Stellarium to find it if you would like to include it in your composition. Stars move faster the nearer you get to the celestial equator and will move in different ways in different directions – try pointing your camera South, East and West for different direction trails.
There are a few methods to create star trails but the one with the most advantages is to take many images with spot stars and ‘stack’ them in post-processing using a dedicated (and free) program called StarStaX. You can use Photoshop to do this, but it will get cumbersome quickly and StarStaX has a special ‘gap filling’ mode which will join up any missed frames.
For this method, since you will be taking so many images, it is imperative to have a lot of space on an SD card (I use 128 MB SD cards) and a fully charged battery. The number of images that you take will depend on how long you want your exposure to be. An alternative approach is to take a very long exposure (typically over an hour and a half or longer) but this would most likely involve the use of expensive neutral density filters and be susceptible to ruin by chance events such as a passing cloud.
A lot of the planning for capturing star trails and setting the exposure is similar to the Milky Way. I suggest the same parameters as for capturing the Milky Way as a starting point. One exception is white balance. It is important to set it manually so that the colours do not change over time. Narrowing your aperture will result in fewer star trails. You can experiment with different effects.
What is different from Milky Way photography is that you need to set an interval timer to take many exposures. The general rule for star trails is that you need to capture images for a minimum of one and half hours with minimal time in between each photo. I took 201 images in just under an hour. You can go for five hours or even longer if you wish. On the other hand, just 10 minutes can give you some short but noticeable star trails.
Setting the interval timer is really one of the most complicated steps. You need to understand how it works on your camera or interval timer prior to setting up your long exposure. After you determine your exposure you then need to set your interval. Suppose that you want to take a series of 15 second exposures, with a gap in between each of 1 second. This one second allows the camera time to write the data to the SD card and avoids it overheating which can cause additional noise.
There are a few things that you need to work out and which are probably specific to your camera. First of all, some cameras have shutter speeds based on the principle of stops. On my camera, a 15 second exposure is actually 16 seconds long and a 30 second exposure is actually 32 seconds long. You may be able to find out how your camera works from its documentation. But if you can’t, just time it yourself.
Next you need to understand how your camera handles intervals, there are two approaches, which are shown in the following diagram:
With approach A, the interval is the gap between the exposures. So you would set it as being 1 second for a 1 second gap.
With approach B (which is what my camera does), the interval is the duration of the exposure plus the gap. Therefore, you would set it at 17 seconds to have a 1 second gap between 16 second exposures. Here you can see why it is important to realize if your camera treats a 15 second exposure as a 16 second exposure.
It is really important to turn off your image review. If you don’t, your LCD display will show an image after each picture and drain your battery very quickly. Also, set a two second delay on your shutter button to avoid camera shake or use a remote trigger. Turn off noise reduction and image stabilization. Remove any filters and attach a lens warmer if you have one to keep dew away. If you have a DSLR then you might want to cover your viewfinder. This is because for long exposures in particular some light can leak into the frame. Just a lens cleaning cloth draped over the top should do the trick. This isn’t relevant for mirrorless cameras.
It is also helpful if you capture a few ‘dark frames’ after your session. Once you take your images, keep the exposure the same, put on the lens cap and take about five images. You will use these in post-processing to average out background noise created by sensor heat.
Once you collect your images and process them, you need to export them all as jpgs. From there you can add them to StarStaX along with your dark frames.
For my star trail image, I wanted to include the cottage that we stayed at in the frame. Since it had the lights on, it would be very overexposed in my star trail images. I therefore had to do a separate shorter exposure for it. Then I combined the star trails and cottage images in Photoshop.
Once you get the hang of photographing the night sky, it is fun to try some different things.
I was lucky enough to be in the countryside at the time comet NEOWISE was near to Earth. I used the Stellarium app to locate it in the night sky. Then I shot it using the exposure method that I had for photographing the Milky Way.
Another fun thing that I did was to use a long exposure and run in front of the camera with a red head lamp pointing upwards to add a light painting effect.
It can be daunting thinking about photographing the night sky. But it certainly is possible with a bit of planning. It’s one of the most rewarding things that I have done photographically. I hope you enjoyed this intro to astrophotography! Have fun and I can’t wait to see what you capture!
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