How to photograph the milky way

 

Photographing the Milky Way is one item on many a photographers 'must do' list. It is rare to see it with the naked eye thanks to light pollution, but our basic DSLR cameras can capture even the faintest Milky Way with the right techniques and a suitably dark location. Read on to learn everything you need to photograph the Milky Way.

The Milky Way, shot at Coru's southern beach. © 2015 diffuse photo

The Milky Way, shot at Coru's southern beach. © 2015 diffuse photo


Equipment needed to photograph the Milky Way

  • A sturdy tripod - the more sturdy the better. (Essential)

  • A DSLR or Mirrorless Interchangeable lens camera with good high ISO capability - needed for a clean, high quality image.

  • A wide angle lens with wide aperture - I recommend 14 mm for full frame cameras (Professional DSLR), or 8 mm for APS-C cameras (most low-mid ranged DSLR).
    Longer focal lengths are OK but will reduce the detail captured. Recommended aperture: f/2.8 or below.

  • A camera remote - Ideal but you can use self timer instead.

  • A torch or head lamp - for working in the dark safely. (Essential)


1. Find a very dark place away from lights

From a busy city location, the light pollution overpowers the weaker star light, blotting out all but the brightest of stars, making the experience far less rewarding. Even in the best locations we want to be taking exposures of up to 20 - 30 seconds to capture the faintest stars. In heavily light polluted areas the light from the street lamps will fill the atmosphere, washing out the photo. So, the answer is to get away from the cities, ideally to a dark sky site to the north of a less populated area.  It can be very difficult to find a suitable location here in the UK, however this excellent resource lists all approved UK dark sky sites: http://www.darkskydiscovery.org.uk/dark-sky-discovery-sites/map.html. Try to avoid a full moon or shooting too close to sunset as these will cause the sky to be bright and make it very difficult to bring out the contrast.

Light pollution from near by cities can make it very difficult to photograph the milky way. 

Light pollution from near by cities can make it very difficult to photograph the milky way. 


2. Know the best time to observe the Milky Way

In the northern hemisphere the Milky Way is visible from March to October. 
In the southern hemisphere you can see the Milky Way from February to October.


3. Know how to find the Milky Way

To locate the Milky Way galactic core you'll need to locate the constellation of Sagittarius. Using a planisphere will help you to do this if you are new to astronomy.

  1. Locate the three bright stars of Orion’s belt.
  2. Turn around about 180 degrees then locate Scorpio and Sagittarius (the "Teapot").
  3. The band of the Milky Way spans from Orion, through Cygnus to Scorpio, and Sagittarius sits at the core where the Milky Way is brightest.

It’ll take about 15 to 20 minutes for your eyes to adjust to darkness before you will see the Milky Way clearly so avoid all light sources and use these brighter stars and constellations to help you pick your shot.  

Alternatively you could use an app to locate your stars and the galactic core. Stellarium tells you where, and when to catch each of the sky’s features which can be very helpful when setting up in advance.

Note: The further north the viewing position, the lower the galactic core will rise from the horizon. Further north than 65 degrees latitude and you’ll be out of luck for the Milky Way, but more likely to catch the Aurora Borealis (Northern Lights).

The core of the milky way can be easily identified by first locating Sagittarius or 'the teapot'.

The core of the milky way can be easily identified by first locating Sagittarius or 'the teapot'.


4. Arrive before dark to set up

Whenever possible arrive at your location before dark. With some planning you should know roughly where to aim your camera and at what time your shot will come into view. Use the daylight to choose an interesting location with some foreground features to add interest to your photograph.

Setting up the camera on a sturdy tripod with remote trigger (cable) during daylight will ensure a quality night sky photograph. Once night falls this task becomes much more difficult. 

Setting up the camera on a sturdy tripod with remote trigger (cable) during daylight will ensure a quality night sky photograph. Once night falls this task becomes much more difficult. 


5. Use a sturdy tripod & Remote trigger

Ensure that have a stable setup with a well placed tripod and that your camera is securely attached to the mount. Any movement or ‘creep’ due to a loose attachment or too much weight on the mount will ruin your shot.

Attach a remote trigger. This will enable you to trigger the camera without risking any camera shake, or accidentally adjusting any settings.


6. Set your focus before it goes dark

Use a very distant object to focus on infinity. Often the infinity marking on the lens will not be one hundred percent accurate. To ensure the sharpest stars switch your auto focus off, and using live view on your camera's screen, focus on something far away. Next, use your camera's live view zoom to see more detail and further refine your focus.
Leave auto focus turned off and note the position of the focus and zoom rings on your lens. This will ensure your focus stays sharp.
Turn off image stabilisation when on a tripod to ensure sharper results.

How do I focus in the dark?

Focusing on infinity after sunset can be considerably more difficult, however sometimes it becomes necessary.
Depending on your camera's low light capability, it is possible to choose a very bright star to focus on. You may have to adjust your exposure settings to be able to see the star in your live view. Do not try to use auto focus or the viewfinder, it just won’t work. If even a bright star proves too difficult to use, perhaps a distant street lamp, or a using a torch placed far enough away will help.

Tip: Note the highest distance on your lens focus indicator or ring, infinity is any distance further than away.


7. Set a long shutter speed

Use a long shutter speed of 20+ seconds.

Taking your photo over a longer period of time will allow plenty of time to gather enough light from even the faintest of stars. There is a limit to the length of time we can expose for however. Since the Earth is spinning, the stars will appear to move across the sky. To keep the stars sharp and point-like and use the longest exposure possible we can use the 500 rule. This is a rule created for full frame professional cameras or 35 mm film. I’ve also included a modified version of the rule for entry level to mid range crop sensor cameras.

For 35 mm professional / film cameras: Max exposure time in seconds = 500 / focal length

Example: 500 / 14 mm = 35 Seconds.

For APS-C cameras Max exposure time in seconds = 333 / focal length

Example: 333 / 8 mm Zoom = 41 Seconds


8. Use a wide aparture of at least f/2.8

The goal of astrophotography is to capture as much light as possible in the limited time available. The wider the aperture of the lens, the more light your camera will capture. So setting your aperture to a wide aperture (low f number) will help. Set the widest aperture possible without losing image sharpness. 

For more info on aperture read the exposure guide.


9. Use a high ISO starting at 3200

The goal is to capture as much light as possible without overexposing. Start with an ISO of around 3200 and adjust the ISO until the most detail possible is captured. You may need to go up to ISO 6400 or further.


10. Check the histogram to find the best exposure

One of the biggest challenges in Milky Way photography or any other form of astrophotography is judging exposure. Since the raw image on the back of your camera is likely to require some post processing to bring out the details, and more so if you are photographing with light pollution, the image on your camera can be misleading.

In order to judge the quality of your exposure you will need to use the camera’s histogram. While previewing a photograph, your camera can display a histogram; a graph displaying the distribution of light in the photograph.

Viewing the histogram, you should see peaks on the graph, if the majority of the peaks are on the left this means your image is mostly dark, and to the right means mostly bright. Seeing peaks all the way to one side or the other usually means you’ve under or over exposed and some of the light couldn’t be recorded. There is usually some tolerance for this, especially if you are shooting in RAW (you should be), however it’s best to play it safe and keep all of your peaks within the bounds of the graph.

The histogram is a graphical representation of the brightness of each pixel. In this histogram there are far more midtone pixels than shadows and highlights. 

The histogram is a graphical representation of the brightness of each pixel. In this histogram there are far more midtone pixels than shadows and highlights. 

Expose to the right (ETTR)

‘Expose to the right’ (ETTR) is a method commonly used by astrophotographers. ETTR is absolutely crucial to anyone photographing the Milky Way with light pollution. ETTR means exposing an image to have most of the peaks as far to the right side of the histogram as possible without falling off the right (clipping).

How does ETTR Work?

Most digital camera sensors do not record light and shadow equally. Due to the way sensors record light linearly then convert the range to a logarithmic scale, about half of the image data effectively occupies the top quarter of the images brightness range. This can lead to poor quality shadows and lost detail when corrected later in post processing if under exposed. You can read the detail about linear and corrected distribution here: https://en.wikipedia.org/wiki/Exposing_to_the_right.

 

Why do we use ETTR when photographing the Milky Way?

In astrophotography, the majority of the image will be dark. By using the ETTR method, we ensure that we have captured the maximum possible amount of light and data from the scene which later we can manipulate to bring out the range of brightness required without detail loss. The noise created by using a high ISO can be at least partially avoided since noise mostly manifests in shadow areas where not enough light was captured. By giving ourselves headroom to dial down the exposure we’re effectively reducing signal noise instead of amplifying it. At the same time, we’re allowing our camera to capture even the dimmest of stars.

Expose to the right (ETTR): With most of the images pixels in the highlights, the peaks on the graph are on the right.

Expose to the right (ETTR): With most of the images pixels in the highlights, the peaks on the graph are on the right.


11. Edit your Milky Way photo to bring out the subtle details

Without going into a full guide on editing techniques, you’ll almost certainly need to process your raw file in an application such as Adobe Lightroom, or Photoshop, although any high quality photo editing software will work fine.

Don’t be put off by the raw file.

Depending on the levels of light pollution and clarity of the sky at the time of shooting, your photo may appear washed out and lacking in contrast and detail. More so if you used ETTR (see above). Raw files need some work to tease out the layers of details stored in those pixels.

Make small adjustments

It’s easy to get carried away, and when doing large contrast adjustments some of the finer details can be lost. Treat your edit like a delicate balancing act of bringing out the fainter stars without loosing the subtle detail.
Note: If you are using ‘dark frame subtraction’ to remove hot pixels and sensor noise, you must do this first as editing will reduce the effectiveness of this technique - see the video below.

Raw Milky Way images will often look very dull and without contrast - this was shot using expose to the right (ETTR) as described above in less than ideal conditions, during a very short window between sunset and moon rise.

Raw Milky Way images will often look very dull and without contrast - this was shot using expose to the right (ETTR) as described above in less than ideal conditions, during a very short window between sunset and moon rise.

Start by adjusting the Exposure

Raise the exposure until the maximum amount of detail is visible and no more. Once you’re no longer seeing more start appearing (not to be confused with the noise) stop raising the exposure. If lowering the exposure due to shooting ETTR, lower until you start to see details disappearing, then back up a little bit. This won’t get rid of the washed out look if you had a bright sky, so bare with that for now, we’ll get onto removing that next.

Adjust the exposure on your Milky Way raw photo until you can see as much detail as possible.

Adjust the exposure on your Milky Way raw photo until you can see as much detail as possible.

Use the tonal curves adjustment tool for contrast

Adjust the contrast using the curves editor to darken the pure blacks without losing the detail in the brighter areas. Making small adjustments adjust the curve for the desired result. Remember, sometimes a pure black sky isn’t always the best look.
This is a powerful tool for isolating the bright stars and dimming the background wash.

Adjust the tonal curves to enhance contrast.

Adjust the tonal curves to enhance contrast.

Edit to taste

Once you’ve revealed the best of the details, edit the photo as normal. Use a natural white balance if you wish to keep the true details aim for a white balance setting of around 4600 and adjust to taste from there.

Noise reduction

Apply noise reduction very lightly. Heavy reduction can remove stars from your photograph. Lightroom’s noise reduction has improved greatly in recent releases, however tools such as Topaz, and DXO Optics Pro offer the best results. Noise adjust with care. In some extreme cases, multiple subtle passes of noise reduction are required, meaning applying small amounts of NR then going over the image again until the noise is dealt with.

Advanced noise reduction - Dark frame subtraction (optional - advanced)

Advanced Photoshoppers can use dark frame subtraction to remove ‘hot pixels’
Hot pixels are bright, over saturated pixels in your image caused by the heating of your camera sensor over long exposures. They occur more in warmer environments but can happen on any long exposure.
To perform a dark frame subtraction you’ll need to put the lens cap back on right after taking your photo and shoot a dark frame of equal length to your main photo. By doing this under the exact same conditions as your Milky Way shot, the noise produced by your camera can be captured, and then removed in Photoshop.
Note: Dark frame subtraction should be done before any additional editing.

This video explains dark frame subtraction perfectly with a great example.