Have you ever had the chance to get away from the city lights on a dark night to stare up at the stars and just observe? To me, nothing beats it, and that feeling is one of my favorite parts of astrophotography. Of course, you’ll also hopefully come away with some beautiful images of the starry night sky as well, and this post is dedicated to helping you get started.
I originally sat down to write about creating a star trails image, but it turned out to be too long for an introductory post so I decided to break it up into a few segments. Naturally, we’ll start with how to take a properly exposed, sharp photo of the stars.
In astrophotography, we’re dealing with super low light conditions, and that’s the main consideration we have to make when setting up our camera’s exposure settings. We need to make sure that enough light is going to reach the sensor so that we have a sharp, well-exposed image.
For this reason, we need to shoot the night sky in manual exposure mode. We’ll start with settings that will get us into the right ballpark, and use our image preview and histogram to get the exposure settings dialed in from there. Each night is a little different, and the moon phase in particular can really affect the brightness of your exposure.
To start, we’ll cover the manual exposure settings. After that, we’ll talk about setting up gear in the field, focusing in the dark, composing a strong image, and then finish with a few more advanced tips.
Exposing for the Stars
With the camera in manual mode, I will usually open up the aperture all the way, or nearly all the way. I also start with a substantially long shutter speed, usually 20 seconds or so. And even with these settings in place, I still usually start with an ISO somewhere around 3200.
A fast lens (with a very wide aperture such as f/1.4, f/1.8, or f/2.8) would be a strong option for night photography. The wider the aperture you use, the more light you will allow into the camera, and generally speaking, a wide open aperture will be the best way to get very sharp stars in your image. That said, I did much of my beginning astrophotography with an f/3.5 wide angle lens so don’t be discouraged from trying, even if you don’t have a very fast lens. You can still make great images at night, you may just need a longer shutter speed and/or higher ISO.
Shutter speed is a little bit trickier. I’ve already mentioned 20 seconds as a very generalized starting point. However, there are two factors to consider when selecting your shutter speed. A faster shutter speed will give sharper stars, but may give too dark an exposure. A slower shutter speed will give a brighter exposure, but after 20 seconds or so, the stars begin to visibly “streak” in the exposure due to the rotation of the earth. And beyond 30 seconds, the stars may no longer look sharp due to the “streaking” effect caused by longer shutter speeds.
There’s a general rule in astrophotography known as the rule of 500, which may help you select your ideal shutter speed. The rule states that your ideal shutter speed (in seconds) should be roughly equal to 500 divided by your focal length (in mm). For example, if you’re shooting with a focal length of 20mm, your ideal shutter speed will be 500/20, or 25 seconds. This should theoretically provide you with the longest shutter speed possible before the stars appear to streak at your given focal length. Keep in mind, however, that this is still just a general rule, and you can always use this as a starting point and make adjustments based on your results in the field.
Next, you’ll need to select your ISO, and in this case you’re mainly just trying to avoid noise in the image while getting the exposure where it needs to be. For images of the stars, you’ll likely need to use an ISO you might normally consider very high, such as ISO 3200 or 6400. The key here is to try to get the image properly exposed, so you avoid having to increase exposure in the dark areas of the image in post production. It’s best to avoid having to increase exposure in post production for high ISO images, because that will cause noise and grain in the image to become very apparent.
On that note, be sure to keep an eye on your histogram while you’re shooting! In such dark conditions, images on your image preview screen often appear much brighter than they actually are because your eyes have become more light sensitive in the dark of night. But your histogram will always give you an accurate reading of your exposure. Also keep in mind that it’s a good idea to take multiple exposures, and to try different exposure settings while you do so. This will give you many options to choose from when you’re back at home working on the images in post production.
And finally, I usually change white balance from Auto to Kelvin mode, so that I can set it manually using the Live View screen. Alternatively, if you don’t have Live View, you can use test images to set a manual white balance in Kelvin, or leave white balance on Auto—just be aware that the white balance may change from one image to the next.
So for astrophotography, the basic exposure settings to start with look something like this:
- Manual exposure mode
- Aperture f/2.8 (or as wide open as possible)
- Shutter speed 20 seconds (or 500/focal length)
- ISO 3200
- White balance K mode (set manually)
Field Work in the Dark
Now that we’ve covered exposure and white balance, let’s move onto getting set up in the field.
As usual, having the right gear always helps! Because of the long shutter speeds required, a tripod is truly a must, so don’t leave it at home. Having a good headlamp will also help if you need to walk or hike any distance in the dark, and can also be useful when setting up your camera or changing your settings. Just be careful because turning your headlamp on once you’re shooting can disrupt your night vision and can also disrupt any exposures in progress (yours or other nearby photographers’). A remote shutter cable will help you to eliminate camera shake. It also never hurts to have a spare, fully charged camera battery and memory card on hand. The last thing you want is to put in all the effort to get out for an astrophotography shoot and have a dead battery or full memory card spoil the fun.
While we’re discussing gear, it’s probably worth noting that full frame cameras and high end image sensors really pay dividends in these types of extremely low light situations. You’ll be pushing your camera gear to the limit, and if you’ve invested in high quality gear, this is one of those instances where you’ll see noticeably improved results.
I’d recommend dialing in your initial exposure settings before you head out or while you’re still in your car. It will be one less thing to worry about out in the dark. Once onsite, you can focus on finding a good composition and setting up your gear.
Focusing in the dark is yet another challenge. Many times, autofocus may not work because of the low light conditions. You can try using autofocus by selecting a distant light on the horizon or the moon if it’s visible. If you’re able to grab an autofocus, confirm that it gives you sharp stars by taking a test exposure, then remember to turn autofocus off so that your camera doesn’t refocus in the middle of your shoot. You can also focus manually if you have a good Live View feature on your camera. To do so, turn on Live View, zoom in on the brightest object in the sky or on the horizon, and manually focus until the object becomes sharp. If all else fails, put the lens into manual focus mode, focus all the way out to infinity, and then dial it back just a touch.
Compositionally, close objects in the foreground will not appear sharp due to the wide aperture and narrow depth of field. There are post production compositing techniques for addressing this (think focus stacking) but that’s a subject for a future blog post. For the sake of today’s post, just keep in mind that foreground objects which are more distant will appear sharper, and objects which are too close may appear noticeably fuzzy.
For this reason, good foreground targets to start with tend to be larger, more distant objects. Think large trees or campsites shot from a distance, big landscapes, mountains, streams, bridges, and such. People also make interesting foreground subjects, so don’t hesitate to either get into the frame yourself or have someone along to model for you.
If you can spot the Milky Way in the sky, use it! It makes for a very dramatic night sky image which you’ll treasure. The first time I photographed the Milky Way, my jaw hit the ground when the image preview screen lit up and I saw my photo. Human eyes don’t see color well at night, but cameras don’t share that problem so you’ll be treated to a dramatic, beautiful, colorful image that looks much different from what your eyes can see!
These are just a few compositional tips and tricks, but feel free to start here and get creative!
There are two applications which are fairly well-known for helping avid astrophotographers plan their shoots: The Photographer’s Ephemeris (TPE) and PhotoPills. Each of these applications is useful beyond just astrophotography, and each could be the subject of their own blog post, but for those of you who want to take your astrophotography planning and execution to the next level I’d highly recommend getting started with one or both of these apps. They are particularly useful for planning Milky Way shots.
There are also a few camera settings you can play with if you really want to make your images as sharp as possible.
Mirror Up mode for DSLRs, or Live View shooting (which also locks the mirror up) will further reduce any camera shake caused by the mirror lifting and dropping when an exposure is taken.
Exposure Delay Mode (set to 1 or 2 seconds) will further reduce any camera shake caused by pressing the shutter release, especially when combined with a remote shutter cable. This setting is also extremely useful if you forget your remote shutter release cable or simply don’t have one.
Long Exposure Noise Reduction is another useful feature if you’ve got a composition and exposure you love. With this setting enabled, the camera finishes taking the actual exposure, then it closes the shutter to create a “dark frame.” This requires the same amount of time from the camera as it takes to capture the original exposure. Thus, it can be time consuming when enabled, because the camera will be disabled for 20-30 seconds after each image. This “dark frame” allows the camera to eliminate noise in the original image created by “hot pixels” and other aberrations resulting from the slow shutter speed. Because this setting literally doubles the amount of time it takes for the camera to create an image, I only enable it once I know that I have a good composition and a good exposure, so that I can get the cleanest raw image possible.
Once you get the hang of taking a sharp, well-exposed photo of the starry night sky, the possibilities are nearly endless. You can shoot star trails sequences, create very cool timelapse videos, shoot the Milky Way, and try new compositing techniques to produce even more dramatic imagery. If these subjects interest you, stay tuned because we’re going to be posting on each of these topics in the coming weeks and months.
In closing, we’d love to hear from you if you decide to give these techniques a try. Drop us a line in the comments or send us an email to firstname.lastname@example.org with your feedback and include your favorite images from your shoot. We always love hearing from our friends and customers, and we hope to hear from you.