Welcome to our beginners guide to astrophotography! Astrophotography is the art of capturing images of the night sky and refining them to highlight features that are usually unavailable to the human eye. It is one of the most technically complex forms of photography, and presents many unique challenges to those just starting out in the genre. Before we begin, it is worth noting that there is a steep learning curve to Astrophotography, and as such, do not expect to learn the practice overnight.
The aim of this guide is not to allow you the ability to master the craft, but rather to act as an entry point, distilling what you need to know to get started into a simplified and easily digested explanation. As such, there are a few pointers that we need to cover before we take a deep dive into the world of Astrophotography.
One step at a time
There is nothing wrong with starting out with merely a tripod and a digital camera, or even a simple Refractor Telescope and your smartphone, particularly if your momentary goal is to capture terrestrial shots, or simple pictures of planets, but you should be aware that the images you capture might not be up to snuff, and that too is okay. Again, this is a hobby where your goal to work your way up, strengthening your skills over the course many months or years.
Unfortunately, you can’t just walk outside and start snapping pictures if you want the best quality in your images. You need to plan your shoot ahead of time. Take the time to figure out what object you want to shoot, and research the conditions that might affect said shoot, such as the area of the sky the object lies in, and plan your shooting location accordingly, so as to limit any problems that might result from nearby light pollution. Make sure that weather permits you to stay outside comfortably for the length of your shoot, and that cloud cover won’t impact visibility. Keep in mind too, particularly with colder weather, that you will need to let your telescope and camera adjust to the temperature before taking any pictures. You will also want to shoot around the schedule of the moon, planning your outings in the days adjacent to the New Moon, so as to have as dark a sky as possible allowing for more contrast. To limit atmospheric complications, you should also try to shoot toward the Zenith, or the part of the sky directly above you, where there will be the least amount of light pollution, and where the atmosphere will be the thinnest.
Although the goal of this guide is to teach, there is no substitute for experience. It is highly suggested that you seek out local astronomy clubs, where many of the members will be able to show you the ropes, let you test out equipment, and will happily encourage your personal and professional growth.
Skillsets
Astrophotography requires experience in a number of different skillsets, which is one of the main reasons that the hobby is particularly difficult to enter into.
Of course, you will need experience in Astronomy, knowing how to operate a telescope, how to locate and focus into your celestial targets, and have the equipment to do so. Experience with, and knowledge of the night sky, will save you a lot of time and headache in searching for targets and knowing which are within the grasp of your equipment’s capabilities.
It is also beneficial to have some understanding of photography, specifically in operating a manual camera. Many cameras simplify the process of photography by automating exposure settings, but because you are aiming to capture images that are either faint or invisible to the human eye, the camera will not be effective at handling this process for you, so you will need to learn to do so yourself. This will require lots of trial and error, so don’t let yourself get discouraged, and always be on the lookout to turn simple mistakes into learning experiences.
You will need to become proficient at image processing, particularly for Deep Sky Astrophotography. The brightly contrasted, colorful images of galaxies and nebulae are not procured in a single image as most photographs are. Rather, they are compositions made through a process called Stacking, where dozens of images are layered over each other, and then the imperfections removed. While most of this is handled by computer programs, it will take some time to learn how to operate them, and maximize the effects that you are aiming for.
Types
There are three main types of Astrophotography:
Terrestrial, or Nightscape, Astrophotography combines traditional photography with the wonders of the night sky. Typically, these photographs will feature unique and charming landscapes in the foreground, set upon a backdrop of mesmerizing celestial imagery—a simple starscape, the moon, or the reaching arm of the Milky Way are common objectives. As with all Astrophotography images, these are best taken with wide-angled long exposure shots, however will not require the heavy image processing that deep-sky and planetary photographs will. This is the simplest form of Astrophotography, and where you should start out, as you can achieve results with simply a smartphone and a telescope, by aligning your phone’s camera with the telescope’s eyepiece, or a DLSR camera and a tripod.
Planetary Astrophotography is exactly what it sounds like—taking highly detailed and focused images of planets, which highlight the planet’s character and features. A little more complex, and where image processing and environmental factors really come into play, Planetary Astrophotography is a great step for beginners to Astrophotography that have experience with operating telescopes. Because the entirety of your photograph contains objects outside the Earth’s atmosphere, environmental factors—such as light pollution, air quality, and weather—become essential considerations.
Deep Sky Astrophotography is by far the most difficult, complex, and labor intensive of the three types of Astrophotography, featuring highly processed images of galaxies, nebulae, and star clusters. You will need to focus your efforts on collecting a series of long exposure shots with a long focal length, to ensure that the features of these faintly lit objects can be brought out in magnificent detail. Deep Sky Astrophotography can easily produce some of the most rewarding and hypnotic images of any kind of photography, although you will need to hone your skills and work your way up to this genre to achieve results that you can be proud of, and is not something to shoot for right out of the gate.
For the best results, each of these genres of Astrophotography require their own equipment specifications, which is one of the main reasons that the hobby can quickly become expensive.
Basic starting equipment
Once you have the resources to invest in an Astrophotography rig, there are three main pieces of equipment that you will need.
Perhaps the most essential piece of equipment is a DLSR camera with manual control capabilities, so that you can customize your camera’s exposure settings to produce the best images. A DLSR, or Digital Single-Lens Reflex, Camera is an absolute necessity to capture deep space images, as a smartphone will not have the capability. However, you will be able to capture Terrestrial shots with only your DLSR, so this type of camera is the perfect starting point. Similar to the way a Catadioptric Telescope is a combination of both Refractor and Reflector Telescopes, a DLSR is combination of traditional single-lens camera design with digital imaging capabilities. If you have the funds on hand, this is the first piece of equipment you should purchase.
You can start off with a dependable Tracking Mount and tripod set up, and as you are looking to upgrade your equipment, this is where you will want to pay the most care and attention, as investing in better equipment here will give you the best return on investment in regards to the quality of your imaging. This is because you will need a tripod that will support the weight of your rig in its entirety, allowing for stable shots where small movements will not jeopardize your imaging. Tracking Mounts are essential so that your long exposure shots do not succumb to an effect known as star-trailing, where the rotation of the Earth creates streaking that trails from each star. Tracking Mounts are mechanized to move along with the Earth’s rotation, at 15˚ per hour, and will need to be calibrated to align with your hemisphere’s Celestial Pole. In the Northern Hemisphere, this is Polaris, also known as the North Star. In the Southern Hemisphere, this is the Southern Cross. As you upgrade your equipment, you will eventually want to build up to a Go-To Mount, which will not only track your celestial target, but is programmed to automatically locate said targets, alleviating much of the labor involved in setting up your shots, and allowing you to get to snapping your photographs quicker.
And, of course, for anything other than Terrestrial Astrophotography, you will need a telescope. Because Deep Sky Photography takes some time to work towards, its recommended you start out with a wide-field Apochromatic Refracting Telescope—compact, if possible, so as to limit difficulties involved with moving and setting up your rig. A wide-field set up will also allow you to capture larger objects, and get the more content in each of your photos. Eventually, you might move up to a Dobsonian Telescope, or if you’ve saved enough, a Catadioptric, in order to get the best Deep Sky shots.
Over time, you can purchase additional filters, lenses, or other attachments as needed, but you can get started without them and still produce fantastic images.
Manual exposure control: the basics
Again, you will need a DSLR camera with manual settings, as automatic exposure controls will work against you. There are three basic elements of your camera that control exposure: ISO, F-Stop, and Shutter Speed.
ISO is an acronym standing for the International Organization for Standardization, which creates standard operating measurements for a camera’s operational capabilities. ISO itself measures a camera’s sensitivity to light, and increasing or decreasing a camera’s set ISO will brighten or darken your image respectively.
A camera’s F-Stop is the numerical value representative of your camera’s Aperture setting. By changing the F-Stop you alter the diameter of your Aperture by opening or closing your camera’s Aperture Blades. The ‘F’ in F’-Stop stands for Focal Length, and for Astrophotography you generally want your F-Stop to be as low as possible. The F-Stop numerical value and the size of your camera’s Aperture work inversely, meaning the higher your F-Stop, the lower the Aperture. This is because the F-Stop number reads as a fraction, so an F-Stop setting of f/1 has a greater Aperture than f/64. A low F-Stop setting will allow the highest amount of light to enter the camera, which is essential for you to pick up faint light objects such as nebulae and galaxies in your images.
Your camera’s Shutter Speed is the length of time that your camera’s shutter is open, and light is available to your camera’s sensor. Long exposure photos are typically what you’re aiming for, meaning that you will have a low Shutter Speed, allowing light to enter your camera for a longer period of time. However, because of the Earth’s rotation, you will need a Tracking Mount to avoid star trails. If you do not have a Tracking Mount, lower Shutter Speed and a higher number of images stacked together can help compensate, as the stars will not have time to move before the shutter closes again.
Determining the proper Shutter Speed for your camera to avoid star trails can be difficult, a general rule has been established to calculate your camera’s maximum exposure time: The 500 Rule.
Put simply, the 500 Rule is a mathematical formula, based on your camera’s Crop Factor—the size of your camera’s lens—and the Focal Length of your camera’s lens. The formula appears as so:
500 / (Crop Factor X Focal Length) = Maximum Exposure Time
An introduction to image processing
There is a lot that goes into producing and refining that perfect shot of Planetary or Deep Sky images, and all of this information presented at once can become quite overwhelming. Realize however, that it will take time and practice working with astrophotography software to perfect this process, which is known as Stacking— the process of layering and aligning a number of different photograph types to bring out your target image while removing any undesired effects within the image.
There are a number of different Image Processing software available. Although some people have used Photoshop, or it’s free alternative GIMP, neither of these programs were designed for Astrophotography, and it makes the process of Stacking much more difficult, especially when there is a free open-source Image Processor designed specifically for Astrophotography, known as Deep Sky Tracker. If you have some extra cash, there are also paid alternatives, but it is recommended that you start with Deep Sky Tracker.
Stacking involves four different types of images: Lights, Darks, Bias, and Flat frames.
Lights are pictures of the object that you wish to capture. When photographing, you want to capture as many of these frames as possible, layering them over each other to draw out and emphasize the light captured by your camera. Typically, you want to aim for enough Lights to so that the exposure time for each image, when added together, equals out to roughly an hour of total exposure time. Doing so will also reduce something called Noise, which are unintended defects that occur randomly throughout each photograph, particularly when photographing with a high ISO and Aperture.
The other three types of frames capture inherent imperfections resultant from the natural process of your camera’s function, as well as effects that are emphasized from the process of stacking, and are then removed from your final image by your Image Processing software to create the cleanest image possible. Taken together, these are known as Calibration Frames. You will either subtract or divide these Calibration Frames from your composited lights, the process of which are simple program functions within your Image Processing software.
Darks are frames takes with your camera’s lens cap on, with the exact same setting and temperature that your initial Lights were photographed with. As there is no night entering your camera’s sensor, the information that is captured is singularly your camera’s random Noise, and will manifest as random grain within the image. Your Image Processor will subtract the Noise captured by your Darks from your composited Lights.
Similarly, Bias frames capture noise resultant from voltage that is applied to your camera’s sensors in order to capture an image in the first place. Because this voltage is not applied equally amongst all sensors, each picture receives a different amount of voltage, and thus each individual pixel will have a different Bias for each photograph. To capture Bias, you want to follow the same process as for your Darks, with the exception of turning your Shutter Speed to the highest speed possible. Doing so allows your camera to capture only the split second that the voltage is applied to your camera’s sensors. Like your Darks, your Image Processor will subtract Bias Noise from your composite.
The final Calibration Frames you will need to take are known as Flats, which are images of a flat field of light. Flats counter an effect known as Vignetting, which is when your image’s border has a darker saturation than the main focus of the image, and is typically caused by the shape of a camera’s lens. Vignetting often occurs in all images to some extent, but is amplified by the process of Stacking, much in the same way that the light from celestial objects are amplified. You can capture Flats by laying a Light Box overtop your camera lens, which will provided an equal dispersal of light into your camera’s lens, but you can also take Flats by banding a white T-shirt to your camera’s lens and pointing your camera at the dawn sun. To do so, you leave your camera’s Aperture and ISO the same as they were when taking your Lights, while setting your camera to Aperture Priority. Rather than subtracting this type of Noise, as with Darks and Bias Frames, your Image Processor will divide your Flats by your Lights.
Stacking is a complex and labor intensive task that can take many hours and requires practice with whatever program you decide to use, but is necessary to produce professional quality photographs, and by the end you will undoubtedly be amazed that you yourself captured such a fantastic shot.
