1. Location, Location, Location.
Try and find a area away from light polluted areas such as large cities. the darkest skies will produce the cleanest shots. I use ClearDarkSky,com for scouting locations.
Time is also a factor. The best time to shoot the stars is highly dependent on the moon phase and the time of year.
If looking to shoot the Milky Way, shooting mid-summer (May thru July), when the galactic core (central region of the Milky Way Galaxy) is traveling through the dark sky above the horizon is optimal. For shooting general star trails, the optimal time is highly reliant on the time of year. In February, shooting at 4 AM is when the stars will be brightest and in September or October, shooting right after sunset will ensure the stars presence in the image.
Moon phases can have the power to ruin your image. Moonlight has the ability to wash out night sky images. If the moon is in any way brighter that the crescent, the colors of the Milky Way will be almost non-existent.
This goes without saying, but shooting at night will require a good sturdy tripod. Long lens and slow shutter speeds all dictate the need for a good sturdy tripod. Tripod tip: weigh your tripod down with a backpack or heavy bag. Most tripods have a small hook on the center shaft to hang a bag from. A good travel tripod for the money is the MeFoto RoadTrip!
3. Use A Cable Release or Self Timer
4. Prefocus on Infinity
Turn off your cameras autofocus, and prefocus on infinity. Autofocus is not reliable at night. You can prefocus, then switch to manual focus thus, locking focus at infinity, I recommend manual focus using live view.
5. Use the mirror-lock-up feature of your camera
Locking up the mirror will great improve your chances of getting a tack sharp image. You would surprised how much vibration a mirror operation can have on your image.
6. Shoot Faster Than you think - Rule of 600
You’ll really be surprised on how fast objects moves in the sky.. In order to get sharp shots without star trails, we need to utilize the Rule of 600. I’m afraid to say, a little bit of math is required. This is because the stars are always in motion, due to the rotation of the earth, and so it’s important that you know how long you can open your camera’s shutter for before the tracking of the stars ruins your shot.
The Rule Of 600 Defined
When using a lens of focal length "L" to take a long exposure photograph of the night sky, the maximum shutter speed you should use to avoid blurring of the stars is 600/L = number of seconds.
The derivation is fairly simple:
The sky rotates 360 degrees in 24 hours, or 0.0042 arc degrees per second. Assuming a full frame camera and a 24mm lens, we have a 73.7 degree horizontal view. Assuming a 24 Mp sensor (6000x4000), those 73.7 degrees are projected on to 6000 horizontal pixels, giving 81.4 pixels per degree. Assuming a 24mm lens, the "rule of 600" gives 600/24mm = 25 seconds exposure.
In 25 seconds the sky will move ~0.1 degrees. For our 24 Mp full frame camera with a 24mm lens, 0.1 degrees translates to 8.5 pixels. By the 600 rule, those 8.5 pixels represent the maximum acceptable movement blur before star points turn into star trails. Of course you will never eliminate star trails- you merely reduce the trail to an acceptable level.
If we were using a 1.6x crop sensor camera, we need to adjust the actual focal length by 1.6 to formula before we apply the 600 Rule. For example: a 24mm lens would need to be adjusted to allow for the crop sensor, thus a 24mm lens is actually a 38mm.
600 Rule For Cropped Sized Sensor Cameras:
Shutter Speed = 600 / (Focal Length x 1.6)
7. Shoot in RAW
Shoot in RAW. You should always shoot in RAW anyway, but for astrophotography this will help give you more control when editing your photos later, particularly for noisier images at higher ISO ratings.
Shoot For Greatness
Go for great images of the night sky. We’re living in a golden age of digital photography. Just ten years ago these simple pictures would have been impossible. Now it is within the reach of any photographer willing to go after it. But don’t stop at just capturing the moon, a few stars, or the Milky Way. Put our world on display, for all to see (it’s out there every night :-)). Include the landscape, buildings or anything that adds interest—and look for opportunities to capture something unique. Most of all, get out shooting!