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There may not be a more challenging subject matter for photographers than astrophotography. When I first began making photographs, I had an elusive and challenging goal which was to make a photograph of the moon.
13 years later (has it really been that long?) I think back and smile at how impossible capturing that photograph of the night sky seemed to me at the time. Back then, the idea of making an image that captured the moon or the stars, and even a galaxy, seemed impossible. I assumed the images would require an expensive camera or some kind of magical photo gear. I couldn’t have been more wrong. In reality, you probably have everything you need to get started in astrophotography right now!
Astrophotography is simply a name for the realm of photography which images astronomical objects and the night sky itself. The moon, stars, constellations, galaxies, and even the sun, are all considered astronomical objects. In this article, you’ll learn just how easy it is to make great single exposure photographs of the wonders to be found in the expanses of the night sky.
You will only need some basic photographic gear and a small dose of patience. Complicated image stacking software and astronomically priced lenses and professional cameras not required. Now let’s get started!
Let’s talk about some of the bare bones gear that you will need in order to make your astro photos.
You need to be able to control as many variables as possible, so shooting in Manual Mode is essential. Bulb capability is a plus, but not required. Bulb mode means that the exposure begins when you open the shutter and continues until you choose to end it by closing the shutter. Bulb mode is a setting which is now available on even the most budget friendly dSLR’s and mirrorless cameras (even some point and shoots have it).
Wide angle lenses are sometimes viewed as the only focal length to use for astrophotography, but that is most definitely not true. The key to solid astrophotography is to use a lens which can let in the most light. These lenses will be rated with a small f-number and are often prime (fixed focal length). While wide angle lenses will give you a sweeping vista of the sky, don’t count out your medium-telephoto lenses.
You simply cannot escape the fact that a reliably sturdy tripod is the foundation on which all strong astrophotographs are built. Unwanted motion is your enemy. You will need a tripod that can support the weight of your camera and keep it completely motionless. Also, the mount on which the camera physically attaches will play a key role in the outcome of your images. Low quality ball-head mounts can sometimes drift under the weight of your camera during long exposures, so keep that in mind as well when choosing your tripod head.
You will have your lens tilted upward for many of your shots, so settling dew can become a problem, especially in the summer months. Be sure to pack at least one clean micro-fibre lens cloth to wipe off any moisture which can accumulate on your lens’ front element during long exposures. This is a small piece of gear that can make or break your photo outing.
Unless you are shooting in Bulb mode, a remote shutter release in not necessary. However, it makes your shooting a little easier, and helps to ensure less camera shake. When not using a remote, set your shutter release on the 2-second timer so that you will not shake the camera by pressing the shutter button.
Now that you know what gear you will need, let’s look at how to go about making your astrophotographs.
Without a doubt, the biggest question about astrophotography is, “How long should I expose my image?” The answer depends on what kind of photograph are you planning to make. The night sky is dynamic. Everything we see is moving, although it may not appear that way to our eyes. I often relate making photos of the night sky to making photos of water. If you want motion blur (star trails) you will need a longer exposure time. If you want to freeze motion (constellations and galaxies) you will need a shorter exposure time.
In my experience, the sweet spot for obtaining workable images of stars and the Milky Way without star trails, is around 15-20 seconds depending on the ISO and aperture (more on that shortly) settings. While there are of course no absolute formulas, a good guideline is called the 600 Rule. It is very similar to the reciprocity rule used for avoiding camera shake during hand-held shooting.
The 600 Rule states that to reduce celestial motion blur, the exposure time should be no longer than the equivalent of 600 divided by a given focal length. Meaning that the maximum shutter time in order to reduce star streaking for a 50mm lens would be 12 seconds (600 / 50 = 12), for a 14mm focal length it would be 42 seconds (600 / 14 = 42), and for a 24mm focal length it would be 25 seconds (600/24). This rule is based on full-frame digital image sensors and will keep star trailing less than 8 pixels wide. If you’re shooting an APS-C(cropped sensor) camera, try using 400 instead of 600 in order to obtain similar results.
The important thing to understand about shutter speed as it relates to astrophotography is that, just as in any other type of photography, longer shutter speeds will result with increased motion blur.
Aperture controls how much light is allowed to enter your camera, and in astrophotography the more light you have to work with, the better your images will be. Shoot your scene at the widest aperture possible. Keep in mind though, that all lenses have ideal apertures, and opening a lens all the way up (largest aperture) often affects overall sharpness. That being said, using a large aperture is almost always desirable, because it allows in the maximum amount of light, which will make your stars brighter and small celestial details more visible.
I shoot the majority of my astrophotography from f/1.8 down to f/3.5 and even f/4. Remember too, that with a wider aperture, precise focusing becomes very important due to the decreased depth of field. Manual focusing is very useful. If your camera has a focus magnification option, use it to zoom in on pinpoint stars or the moon, so that you can obtain the sharpest focus possible. Don’t rely on the infinity focus markings on your lens (they are often not accurate).
Selecting the ISO for your astrophotography is an exercise in compromise. High ISOs are better for shooting in low light conditions, but will also result in more grain and noise in your final photograph. Finding a comfortable medium can be difficult. Shoot with the highest ISO that you feel gives you the least amount of noise, but still allows you to use your desired shutter and aperture settings.
Most cameras now have high ISO noise reduction built into the their on-board software. I find it is almost always helpful to turn this function off – stay with me here. The reason being, is that image post-processing software today almost always does a better job of reducing noise than does in-camera high ISO noise reduction, which can sometimes reduce contrast and image sharpness. I highly recommend that you experiment with your particular camera and find out what you prefer for your own needs.
You may have heard the benefits of shooting in RAW format. In astrophotography, shooting your images in RAW format becomes extremely helpful. The extra information gathered from these larger files will add a huge amount of dynamic range, which will allow you to process the images to a greater degree. Noise reduction will also work more effectively when coupled with the RAW image format.
While the objects found in the night sky are incredibly beautiful on their own, adding additional points of interest will often make your astrophotography even stronger. Add reference points such as trees or buildings. Look for a elements that bring harmony within the composition, and flow well with your astrological subject.
While dark skies are certainly ideal for astrophotography, don’t feel that that all external light sources are a bad thing. Sometimes having city lights, or other luminance, interact with your scene can heighten the impact of your composition and add contrast within the image.
Astrophotography loves color. Don’t be afraid to increase, and manipulate saturation and hues in your post-processing workflow. Experimenting with colors will make your photograph a piece of personal art, rather than just a representation. Still, it is advisable not to over process your images so much that you lose detail, and/or make the entire image gaudy and unrealistic (which of course is very subjective). As always, less can sometimes be more.
Astrophotography is challenging, fun, rewarding, and educational. Making images of the heavens is a great way to develop your skills as a photographer, while at the same time producing beautiful images of things that most people may not have noticed before. Today, cameras and imaging software make it easy for us to make great photographs of the night sky. The information you have read here will put you well on the way to producing exciting astrophotos. Shoot for the moon!