Getting Started with Wide-Field Astrophotography: A Detailed Resource Guide
Astrophotography concentrating on vast nightscapes such as the Milky Way arching over a landscape, or photographing beautiful galaxies is by far the easiest and most gratifying way to get involved in the hobby. In no way does it mean a telescope or an equatorial tracking mount is necessary. With proper planning and a few things that you probably already have, the amazing results are completely doable.
1. Minimal Equipment Checklist: Beyond the Basics
Firstly, the camera that you use for capturing the night sky must be able to control the three most basic photographic parameters: shutter speed, aperture, and ISO manually. This condition is absolutely necessary because the automatic modes will not work in such extremely dark places. Any modern DSLR or Mirrorless camera, or a recent model smartphone with a dedicated “Pro Mode” can be used for this work effectively.
Your lens is the single most important element. The reason is that you want to capture as much faint light as possible in as short a time as possible and that requires both a wide focal length and a wide aperture. A wide angle lens, which is generally between 14mm and 35mm, is the minimum necessary to cover large celestial bodies like the Milky Way core. More importantly, the lens should be “fast,” that is it should have a large maximum aperture, preferably f/2.8 or more (f/4.0 is usable but less efficient). The wider the aperture, the more light is allowed to hit your sensor per second and thus you are able to take shorter exposures which result in sharper images with less noise.
A tripod is basically a must have. As you will be making exposures that can last up to 30 seconds, any small movement will be enough to spoil the resulting image. Your tripod has to be stable, strong, and able to hold your camera safely at any angle, even vertically. In the end, a remote shutter release is very close to being a necessity. Even slightly, pressing the shutter button manually, thus causing vibrations, which can blur the final image. A mere cable release, or the camera’s built in 2 second self timer, which allows the shutter to be released without any contact, thus the vibration is eliminated, is the way to guarantee that the exposure will be started in the sharpest way possible.
2. The “Rule of 500” and Sensor Crop Factor
Stars should be recorded as stars and not as short streaks of light traveling on stars (star trails) to demonstrate that you have to take into consideration the Earth’s rotation. The Rule of 500 offers an easy way to work out the greatest shutter speed in seconds that yields the appearance of star movement to be so slight that it is hardly noticeable. The calculation is quite simple:
Maximum Shutter Speed (seconds)=500Lens Focal Length (mm)
Thus, the use of a 20mm lens on a full frame camera gives a maximum exposure time of 500/20=25 seconds. It is better to round down a little to 20 or 25 seconds to be sure that stars are pinpoint.
Understanding this rule is important as it is derived from the traditional 35mm film format or a modern full frame sensor. In case your camera has a smaller sensor, for example, an APS C (with a typical crop factor of 1.5× or 1.6×) or Micro Four Thirds (with a 2.0× crop factor), the stars’ apparent motion will be bigger. Thus, you have to modify the deciding factor by first multiplying the focal length of your lens with the crop factor of your camera and then dividing it by 500 as usual.
Maximum Shutter Speed (seconds)=Focal Length (mm)×Crop Factor500
To illustrate, the use of the same 20mm lens on a 1.5× crop sensor camera will make the effective focal length to be 30mm (20×1.5). The maximum shutter speed will then be 500/30≈16 seconds, which is quite a lot less than the 25 seconds that would have been allowed by a full frame camera. Making this adjustment is absolutely necessary if you want to have stars that are really sharp and of pinpoint size no matter what camera system you are using.
3. Planning and Location Tools: The 50% Rule
Astrophotography images can be of very low or high quality, the latter being attributed to the combining of an impeccable technical execution with as much planning and location scouting. A virtual planetarium application like Stellarium should be your first tool in the outdoor adventure kit (free desktop application or a mobile app). Precisely setting your location, date, and time on Stellarium, you get to see the exact position and orientation of the objects in the sky, e.g. the core of the Milky Way, constellations, and planets.
Without a doubt, this is the most important step in composing your shot, enabling you to figure out at what time of the night the core will emerge from behind your chosen landscape element (mountain, tree, or rock formation) and thus take a picture. The most wanted target, the Galactic Core of the Milky Way, can only be seen at night during certain seasons and hours.
After that, the consultation with a Moon Phase Calendar is a must. The illumination of a Full Moon is extremely bright that it makes it very difficult to see the deep sky objects and the Milky Way that are naturally very faint. So if you want to capture the best detail, you have to go for the New Moon phase which is the time when the Moon is not visible at all, or you can decide to take your shoot during the night when the Moon is under the horizon. The contrast between a Moonlit sky and a New Moon sky is an absolute one.
Finally, you must assess Light Pollution. Resources like Lightpolutionmap.com First of all, these maps show the darkness of the night sky as measured by the Bortle Dark Sky Scale, which is a 9 level system quantifying brightness of the sky. Bortle Class 1 or 2 is clean, really dark places where you can see the Milky Way so bright that it even casts shadows, thus, is the absolute best accomplishment. Almost all towns and cities are between Bortle 6 and 9 classes, in which the sky is lightened, and no trace of the Milky Way can be seen.
Your target city should be the one with the lowest Bortle number meaning Bortle 4 or lesser, as consequently, the less light pollution, the better the quality, contrast, and color of your stacked image will be.
4. Free Image Stacking Software: Signal Over Noise
Astrophotography depends on a very essential procedure known as image stacking or image integration. The method is about shooting the night sky many times with the same exposure settings, usually from 10 to 30 times. Each single frame contains a strong astronomical signal but it also has some random electronic noise, which is sometimes visible as graininess or “hot pixels.” When these pictures are stacked, the unchanged astronomical signal is therefore perfectly aligned and strengthened, whereas the random digital noise is averaged and thus removed. The final image has a much better signal to noise ratio it is cleaner, smoother, and can show a lot more detail than a single exposure could.
DeepSkyStacker (DSS) is the veteran, powerful, and easy to use free program for Windows that specializes in this process. DSS automatically detects hundreds of stars in your individual frames, mathematically aligns them all down to the sub pixel level, and then combines them into one high quality, low noise TIFF or FITS file. It is the gold standard for pure sky stacking, even for wide field images.
Sequator It is an excellently suggested free substitute that is very user friendly for landscape astrophotography on Windows, in particular. What sets Sequator apart from the rest is its intelligent approach to handling the sky that moves and the ground that stays still. A user can sketch a basic mask to separate the sky from the earth, and thus, Sequator can align and stack the stars in the sky while at the same time, it can keep and stack the ground without any movement. In this way, both the foreground (trees, mountains) and the background (stars) become noise free and of high quality, without the need for complicated, separate post processing steps.
For a completely different effect, StarStax StarStax is the dedicated, simple to use free software that lets you make impressive Star Trail images with ease. Rather than aligning and averaging the pictures for noise reduction, StarStax uses a Lighten Blending Mode to blend the pixel data from single to multiple exposures. This mode guarantees that the brightest pixel from any exposure is kept, thus it results in continuous, bright light streaks across the sky along with the dark areas being preserved. Moreover, StarStax has the very important Gap Filling feature that can fill small gaps in the trails caused by the camera’s slight delay between sequential exposures, thereby providing a smooth, beautiful final trail image.
