The procedure is likely to depend on whether you want to photograph star trails, short-exposure astrophotography, or long-exposure astrophotography. Star trails are relatively easy to capture, but astrophotography has to be done with a little more care during short and long exposures. These tips assume that you are using a DSLR.
To make high-quality star shots, you need the right equipment. The equipment may change depending on the type of photography. In general, however, you need the following:
- Stable tripod
- For star trails or short-term exposures, every decent tripod is ideal
- Long exposure requires an equatorial tracking mount
- High ISO Camera
- Although a camera that supports a high ISO value (3200 or higher) is not essential, it generally has better ISO performance, reducing noise at longer exposure times
- Cable release with lock
- When you release the shutter-release button, camera shake will be removed by pressing the Shutter button and should be exposed for more than 30 seconds
- Fast lens
- A fast lens is not an absolute requirement, but you can pause and sharpen the image without restricting the light too much
- Additional batteries or battery grip or power supply
- Long exposures can really absorb the battery power and bring extra batteries.
- If you want to take hours and hours of recording, a battery grip that prolongs battery life is essential.
- It may not be possible to take really long shots (eg 2-3 hours) with a digital camera without a power adapter.
Another requirement is a moonless sky.
Capture star trails
The recording of stars is pretty straight forward. They will not track the stars across the sky, so no equatorial tracking mount is required. To capture star trails over a landscape, you must expose them over a long period of time, from several minutes to half an hour or more. A camera with good ISO performance will be very helpful here as very long exposures can heat up the camera sensor and cause a higher noise level than you normally would. An ISO setting of 100 or less, preferably 50 or 25, would be best.
Aim your camera at the tripod before shooting and adjust the frame. You should use a battery grip or, if possible, and a power adapter to make sure you can take very long shots. Make sure you really like the composition, because it may take 30 minutes to several hours to see the result and try again. Remember that you will probably have to experiment for a while (ie, several nights) before you really get the hang of it and get a decent shot. This is just part of the process (I have not yet done a startrail shoot that I really like myself, and I was there every moonless weekend that I've had for several months.)
Once you've taken your picture, you'll need to configure your camera. It is best to use manual mode for full control. Set your aperture to about f / 4, your ISO to 100, and set the shutter speed to BULB mode (most digital cameras do not measure shutter speed for more than 30 seconds, and BULB mode takes longer). Attach the cable release, and activate the mirror lock mode, if any. When finished, press the release button on the cable release and lock it. A cable release that supports automatic timing is a big plus here because you can set a time, such as 30 minutes or 2 hours, and then go to sleep when needed. If you can not afford a timer release, a basic lockable cable release will do. All you have to do is keep track of the time and manually unlock when your time runs out.
I recommend starting with 30-45 minutes, experimenting a bit and checking the results. With a laptop, you can export the images to greatly enhance the experimentation phase, as it can be difficult to really measure the results on a camera display screen. From this point on it is a question of experimentation. Shorter exposures are generally darker, star trails are short, but they are very clear. For longer exposures of up to an hour or several hours, the landscape around you may be exposed to near daylight, and your star trails may be very long, possibly 130 degrees for several hours of exposure. If you want to record a very long exposure time of several hours and have the ISO settings below 100, I would try to use them and see what the results look like. If the picture becomes too bright, adjust the aperture. An aperture of f / 5.6 or possibly f / 6.3 may be required to keep the ambient lighting at an appropriate level after a long exposure.
To get really long star trails, it is better to expose with an intervolometer so you can take many shorter shots that are just a moment apart. Stacking several photos of short start trails leads to a single image with very long take-off trails. The clarity and brightness of stacked startrail images are usually better than single exposure startrail images. To stack properly, you probably want to use a tool like DeepSky Stacker or IRIS Astronomical Imaging tools.
Taking short-exposure shots at night (Star and Milky Way)
Another form of astrophotography is the short / milky way photograph. Like star trails, they also need a standard tripod, but use a higher ISO and a larger aperture. Fast lenses are extremely helpful here. They definitely want a moonless night to capture a decent sky. Set up your shot as you would for star trails, but set your ISO value to 800 or so and open the aperture wide. A 1: 2.8 aperture lens is helpful, but a lens with a wider aperture of f / 1.4 or 1: 1.2 is even better. Speed is important here to achieve saturation without star trails. If you want to take zoomed pictures with a telephoto focal length, use a lens with a 1: 2.8 aperture. Otherwise, you will have difficulty avoiding tracks. In general, wider angles are better than telephoto lenses. The more you zoom, the clearer the movement of the stars becomes.
Shoots intended to capture the sky without star trails need to be shorter. Once your shot is focused and focused, I would set the shutter speed to 10-15 seconds. Re-use the mirror latch and cable release to open the latch. Since your exposure times are much shorter here, you have much more time to experiment. You can try shutter speeds of up to 30 seconds. However, you are likely to see footprints in the area. Keep an eye on your noise and adjust the ISO setting and shutter speed accordingly. Noise from higher ISO settings (i.e., 1600, maybe even 3200 or more if you have extremely high ISO performance, such as a Canon 5D Mk II) can be a big problem or not if You get a lighter exposure. A good night sky capturing many stars may not have any visible "noise" due to the fine, pixel-like, dot-like nature of the stars you are photographing.
Again, experimenting is the key here. You will have much more opportunity to experiment with the much shorter exposure times, so use them as much as you can.
Take long exposures at night
Long exposures for sky shots require slightly more equipment and care than the other two forms. To capture long shots of the sky without star trails, a special type of mount is required. An equatorial tracking mount is one that works right once to adjust, Tracks the stars with high accuracy over the sky, so you can take several minutes without getting traces.
Shooting with a long exposure generally uses a higher ISO than shooting with stars, but is likely to be less than short exposures. I would try an ISO setting of about 400, possibly 800. As you track the stars across the sky, you have more flexibility in the iris. You can choose to shoot wide open or stop in 1/2 or 1/3 increments. If you shoot wide with an ISO of 400, start with a shutter speed of 5-8 minutes. If you use a higher ISO value, you can reduce the shutter speed, unless you want to make a saturated recording. Apertures between f / 2.8 (or wider) to f / 5.6 are probably the most useful. Stars are point light sources and are especially prone to diffraction. Avoid very narrow openings. I would avoid going below f / 5.6 unless your sensor is very large with very large photo pages. Always use your cable release with mirror lock.
Experiment as always. You may need to set Equatorial Assembly a few times to get it right the first time. Once set, you have plenty of flexibility to experiment. A camera with very high ISO performance, like the Canon 5D Mark II or 7D, significantly improves the quality of your recordings and offers you more options. Taking pictures with higher ISO settings such as 1600 or 3200 can improve the types of pictures you can take and increase the number of stars you can record in a single shot.