Portfolio ~ AstroScapes (The Night Sky)
A collection of digital imagery by Ashley Corr Photography ~ Click a thumbnail to view the corresponding gallery
(29 Images )
In The Field
Camera Equipment & Settings
Full Frame Sensor
Photographing the night sky is not difficult, but it is one field of photography where the right equipment absolutely makes all the difference. Getting sharp photos of dim moving objects like stars and the Milky Way is a lot more demanding than well-lit subjects during the day or with artificial light. A good baseline exposure for the Milky Way on a full frame sensor with dark skies is 14mm, f/2.8, ISO 4000, 25 seconds, and then tweak your settings from there.
Sensor technology continues to improve with every new generation, getting more sensitive with less noise at high ISOs. Generally, full frame cameras have an advantage over crop sized and smaller sensors due to the size of each pixel being larger and able to capture more photons in the same time frame. Sensor size, pixel density (number of megapixels), and in-camera processing all determine the quality of image at high ISO. You want a camera that can shoot cleanly to ISO 2500 at least, and preferably ISO 3200 to 6400 for very dark skies. Some newer mirrorless and crop sensor cameras are quite capable of this, particularly by Sony and Fuji.
Focal Length / 500 Rule
Wide angle lenses let you use longer exposures at night without stars streaking. A frequently used rule of thumb is to divide 500 by your focal length for the maximum number of seconds you can use for an exposure and still get acceptably sharp stars. It’s a relative figure—stars don’t appear to move as fast near the north star, but the further away from Polaris and the closer to the equator you get, the faster the stars appear to move. If you don’t have a 35mm full frame sensor, divide again by the crop factor (1.6 for Canon crop sensor DSLRs, 1.5 for Nikon crop sensor DSLRs, and 2 for some mirrorless cameras). 14mm to 35mm on a full frame sensor is best for Milky Way photography. 50mm and higher usually need a tracker to avoid streaking at long enough shutter speeds.
Here are some examples:
500 ÷ 14mm on a full frame sensor = 35 seconds
500 ÷ 24mm = 20 seconds
500 ÷ 18mm ÷ 1.6 for a Canon crop sensor = 17 seconds
500 ÷ 50mm ÷ 2 for a mirrorless sensor = 5 seconds
Sycamore Gap, Hadrian's Wall, Northumberland, UK
I often subtract another 5 to 10 seconds from these estimates to ensure sharp stars when shooting along the horizon, especially when printing larger than 12" x 18" from a high resolution sensor. For time lapse and star trails a small amount of streaking won’t matter.
A wide aperture of at least f/4 is best for Milky Way photography, preferably f/2.8 unless your camera is capable of extremely high ISOs. Not every lens is sharp at f/2.8, and many f/1.4 and f/1.8 primes are not sharp enough until stopped down to at least f/2. Many lenses produce oblong and pear shaped stars in the corners at wide apertures, this is known as coma and is not easily fixed in post-production. Distortion and vignetting are much easier to fix. A few notable lenses are exceptional at wide apertures with very little coma, particularly the Nikon 14-24mm f/2.8, Tamron 15-30mm f/2.8 VC, Rokinon 14mm f/2.4 SP (manual focus), and Tokina 11-20mm f/2.8 Pro DX (for crop sensors). Generally speaking, lenses with an aspherical lens element have better coma control.
As mentioned previously, ISO 2500 to 6400 is a good ISO range for the Milky Way with dark skies. Conventional wisdom would dictate using as low an ISO as possible for less noise, but night photography is very different. Unless you are using a tracker or stacking images for longer exposures, we have to use very high ISOs to capture enough detail of the Milky Way. Ideally you are aiming for -6 to -7 EV exposures for good Milky Way details with no light pollution or moonlight.
http://photonstophotos.net/Charts/PDR.htm is a good resource for suggested low light ISOs of various cameras.
Ian Norman has an excellent article on finding the best ISO to use for your camera too:
Many Nikon and Sony cameras are highly ISO invariant, where the ISO doesn't really matter very much. You can adjust exposure in post-production and get about the same amount of noise as adjusting the ISO in camera, at the expense of dynamic range. Here is an article by Spencer Cox on that topic:
White balance won’t affect RAW files, just JPEGs, TIFFs, and the preview image on the camera’s rear LCD display. I find a proper white balance is useful when shooting in the field though to get a better preview of my image and exposure, since the histogram won’t be of much use for really dark scenes. A manual white balance of somewhere between 3000° and 4000°K is best for the Milky Way. I’m usually around 3450° or 3570°K on my Nikon. It doesn’t have to be precisely accurate, you can change it in Lightroom or Camera RAW later. If shooting timelapses and editing using LRTimelapse, a manual white balance is preferred for consistency over auto white balance.
The brightness of the rear LCD on your camera will probably be way too bright for reviewing images at night. It will fool you into thinking your photos are exposed brighter than they really are, and it will annoy others shooting near you! I dial it down until I can barely see the difference in shade between the two darkest colors (black and dark gray) in the sample palette, about -2 to -3 on a Nikon.
It’s a good idea to cover your viewfinder or close the curtain to it for long exposures at night. During the day stray light through the viewfinder usually only affects your meter reading and not the image itself, but during long exposures at night it can show up on the edges of your frame, particularly if you have a light source behind you or a headlamp or flashlight hits the back of your camera. Many cameras ship with a little plastic cover (that soon gets misplaced), sometimes on the camera strap. You can also cover your camera with a hat, coat, etc.
RAW versus JPEG
RAW files store much more data than JPEGs, which is important for good post-processing later of night photos, particularly the Milky Way. If your camera has a choice between 12 or 14-bit RAW files, go with the highest quality and image size possible for better noise reduction and shadow boosting later.
There are two types of noise reduction in your camera’s menu: high ISO noise reduction and long exposure noise reduction. High ISO noise reduction doesn’t apply to RAW files, only JPEGs and the embedded preview image, so I leave it disabled to avoid extra processing time by the camera. Long exposure noise reduction applies to all file types and removes hot pixels from sensor heat during long exposures (typically 1 second or longer on most cameras). It doubles your exposure time and shoots the second photo with the shutter curtain closed, then removes any exposed pixels it finds in the second shot from the previous one before saving the file.
For a 30 second photo, a minute isn't a long wait, but for a 4 to 8 minute ground exposure, it can feel like eternity! Night photography is a craft that takes a lot of patience to master though, and I usually leave long exposure reduction enabled unless I’m shooting a panorama or timelapse. If you are shooting a panorama or especially a timelapse for star trails, you can’t have a long interval between shots for long exposure noise reduction. Instead, you can shoot a “dark frame” at f/22 with a lens cap on to capture nothing but hot pixels, and then apply it to your light frames later. Pixel Fixer is a great program for this if it supports your camera model because it can work on RAW files. Other programs like Sequator, Starry Landscape Stacker, and StarStaX can also use dark frames as TIFFs. More dark frames make for better analyzing, but not every program can do this. I usually shoot somewhere between 10 and 30 dark frames for every shutter/ISO combination that I used during the night, if I’m not using long exposure noise reduction in camera.
Blackgang Chine, Isle Of Wight - August (12:10 am)
Critical focus is necessary for sharp stars. Infinity is usually not where it is marked on your lens. Autofocus on most cameras will not work on dim stars. The best method is to manually focus on a very bright star using live view on a tripod. If you have good enough eyes, you can roughly center a star in the viewfinder and then switch over to live view. Live view won’t see any stars until at least 5x usually, and then you can pan around a bit until you find it and zoom in again to 10x or higher. Don’t zoom with your lens, most zoom lenses have “focus breathing” where they shift focus slightly as you zoom. Manually adjust your focus until the star in live view is as small a pixel as you can get it with no soft edges or halos around it. Make a note of where this point is on your depth of field scale and tape your lens down for the night with masking tape or anything that won’t leave a sticky residue, unless you are going to do focus stacking later. If you use qDslrDashboard on your smartphone or tablet, there is a live view filter called Canny that can help focus the outline of stars. Make it as small a circle as you can. I find this easier than using the smaller LCD screen on the camera and trying to see a pixel. The best method is to use a Bahtinov Mask filter. It's very fast and easy to set your focus with no guess work. Ian Norman sells them on his website here: http://www.lonelyspeck.com/sharpstar/
Aurora Borealis (Northern Lights)
Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights), like the Milky Way, are best seen during a new moon with little artificial light pollution, although I have seen them strong enough to photograph during a full moon (that is rare where I live). Both take place over the polar regions and the closer you get to the equator the less visible they are. The Northern Lights are more popular due to more geographical land masses to view them from, but the Southern Lights are no less intense or beautiful. Similar to the weather, they are not predictable very far out in the future (a week at most really, and only accurately to a few hours). This is mostly because the intensity of the lights are heavily dependent on Earth’s magnetic field, which fluctuates unpredictably. There are three measurements used for aurora reporting: Kp, G-scale, and Bz. Kp is an index from 0 to 9 and measures the intensity or strength of the aurora and how far the oval reaches on the globe, with higher numbers being further distances from the poles. There is a G scale of five levels indicating storm levels with G0 being none at all and G5 being an extreme storm. G1 through G5 equate to KP5 through KP9, and you’ll find either number reported with various apps and websites. Finally, there is the Bz, which is the strength of the Earth’s magnetic field in the north-south direction. Positive numbers are northward, and negative numbers are southward. For the northern hemisphere, this means that a positive Bz will deflect most solar activity before it has a chance to interact with our upper atmosphere, resulting in a weak Aurora Borealis. A low Bz in the negative numbers means a weaker magnetic field on the northern pole, and thus much stronger northern lights. Many aurora apps only report the Kp or G-scale, which is not very useful without the Bz. In fact, I find the Bz to be more important for my area than the Kp. I’ve seen strong Kp7 and higher with a positive Bz that resulted in no observable aurora with my camera, and I’ve seen very weak Kp2 or Kp3 with a very negative Bz that resulted in beautiful green and red spikes in the camera!
Souter Lighthouse, Marsden, Tyne & Wear, UK - March (9:20 pm)
The camera captures a lot more than the naked eye can see. The human eye does not see a lot of color at night. We see green aurora the best, but it looks faint white. Red and blue really can’t be seen at all, although the camera will capture it. So you really have to take some test shots with your camera to see what’s out there and don’t rely on just your vision. A good friend and fellow night photographer, Mike Taylor, wrote an excellent article on this topic that I recommend reading:
Camera settings vary wildly depending on the moon phase and brightness/speed of the aurora. When it is moving rapidly, you need a very wide aperture and shorter shutter speeds of 5 seconds or less. A prime lens of f/1.4 or f/1.8 is best in those circumstances. When the aurora is moving slowly you can get away with f/2.8 to f/4 and longer shutter speeds. ISO will range from 400 to 6400 depending on all the rest. It’s a good idea to experiment and try several exposure combinations as the brightness and speed of the aurora will likely vary while you are shooting.
The Milky Way changes orientation and elevation throughout the year as the earth pivots on its axis during our seasons. Here in New England, the galactic core rises from the horizon around 132° on the compass dial in the early morning hours before astronomic dawn in the spring, and the Milky Way forms a nice low panorama in the sky. By summer it is visible for much of the shorter nights but is oriented up and down and passes directly overhead around midnight or a little later, about 165° to 212° on the compass dial.
In the fall the galactic center is visible right after astronomic dusk and sets below the horizon very quickly, still standing straight up and down and passing directly overhead, from 206° to 228°. In the winter, the dimmer portion of the Milky Way (one of the spirals we live in), passes directly overhead and settles into a very wide arch around 180° of the horizon. Quite often light pollution on the horizon prevents you from getting a very good panorama of it though. It’s easier to see this by changing dates and times in Stellarium or PhotoPills than capturing it in a photo, but here are two examples...
Lodore Jetty, Derwent Water, Lake District, UK - April (1:05 am)
St. Catherine's Oratory, Isle Of Wight, UK
September (9:10 pm)