The night sky is variable. Some nights are grey and overcast, some filled with stars, yet others are busy with the movement of clouds on weather fronts. Long shutter speeds are the key to capturing imaginative and beautiful images of the sky at night, so be patient and this kind of photography will become second nature to you.
Due to the Earth’s rotation about its axis, it seems that the light from stars moves in circles around the celestial pole. These movements are detectable after about 5 to 10 minutes, and can be traced by your camera in the form of a streak. To photograph this magical effect, you need a sturdy tripod and lots of patience. Focus the lens to infinity and set the camera’s mode at Manual or Bulb shooting mode. With the use of a cable release you will capture the stars moving across the sky. These exposures can be a few minutes to several hours long. If you keep few things in mind, such as the timing, composition, and power of the battery, you can make photographing star trails simpler for you.
Find the Right Location
The best place to view and photograph the night sky is in the rural countryside because cities have artificial lights which cause a phenomenon known as light pollution. You need to get away from artificial lights in order to see the stars well. A truly dark sky is preferred, but artificial lights keep the night sky from being truly dark. Many beginners aim at capturing the longest star trails by keeping the shutter open for long periods of time. However, they tend to underestimate the impact generated by ambient light in the sky, which can be hard to notice at times. In addition, residual light (such as moonlight) can have a devastating impact on long shutter speed photos. This is because when you keep the shutter open for say, nearly 20 minutes, an hour after the sunset, the camera may perceive it as a day shot. Similarly, a full moon night photo with an exposure time of around 10 minutes could also look like a day shot. Therefore, it is best to attempt such a picture with either a new moon, or well before the moonrise or after the moonset. The light emerging from the stars would be more evident at this time and the picture would be perfect.
Use Long Shutter Speeds
When photographing the night sky with a long exposure, exposures of 15 minutes or longer will show the rotation of the Earth. You’ll need a wide-angle lens and a sturdy tripod, of course. You’ll want to use a cable release to eliminate camera shake of any kind, as it will RUIN your photo. Focus the lens to infinity and set the camera to B "Bulb" shooting mode. Set your aperture to f/4 for optimal results, and depress the remote to open the shutter. You should keep your ISO at 100 to keep the digital noise at a minimum, because the sky is so dark and less prone to producing digital noise when the exposure is above 15 seconds. To complete the photo after your desired elapsed time, depress the remote again, and release the shutter.
Auroras and Polar Lights
Photographing the atmospheric phenomenon of aurora borealis is a challenge for photographers. This difficulty is due to frequent spectacular changes in the brightness of the light. The charged solar particles move very fast and sometimes get hidden making it impossible to shoot them. However, if you follow these tips, you will be able to get the best aurora borealis photos. Anchor your camera on a strong tripod to keep it steady for longer exposures. Set the ISO at the range of 100 to 400. Shutter speed can be as long as 30 seconds depending on the amount of light available. Do not rely on the built-in light meter, which is better left for day time use. Although any kind of lens will do for aurora borealis photography, you should choose a wide-angle and faster lens.
As the light begins to fall, look at the cloudy skies. Watch the colors and how they merge though the cloud. Even though it is dark, you should try using an 80A blue cooling filter to enhance the blue cast of the sky and to reduce the yellow cast from the artifical lights. Use a wide-angle lens and opt for longer exposures. You can first try a few test shots, and then assess them carefully on your digital camera. You should be able to decide on the best range of exposures to capture some good photographs of an overcast sky.
Metering after dark can be a problem, so make sure you choose the best option for your particular situation. If the conditions are both light and dark you need to use spot metering for an accurate reading. If the darkness is even you can use center weighted or evaluative metering. Don’t use flash if you can help it as this can affect the resulting image, creating an area of the photograph that is over-lit. Manual and Bulb modes are the best shooting modes for this kind of photography.
Night skies should always be photographed with the assistance of a tripod. Don’t forget to buy a cable release or a remote control for taking the picture – this is important because some shots will take up to 30 seconds or even more. Your lens ideally should have an infinity focusing mode and your camera should have the ability to do a mirror lock up - a feature in which the mirror in the camera moves out of the way before the shutter is released. This feature eliminates the vibration that occurs when the mirror slaps up into the camera housing. A wide-angle lens is the best choice for night skies, and a zoom makes it even more versatile.
When taking pictures of the night sky, remember that patience is as important as is the ability to look at an image’s composition critically and decide what you need to change next time to make it better. As we stated earlier, the process of finding the right exposure length for the image you want is going to be a process of trial and error (in terms of lens length, shutter speed, aperture setting, as all three allow for different effects). With long exposures of over 30 seconds, a cable release is necessary to ensure tack sharp final images. For additional variety and perhaps better photographs of stars in the sky, you might want to try a few B&W shots. Dress warmly if the weather is cold, because sitting still on a cold night is much colder than walking in the cold, so extra layers may be needed. Remember to take a flashlight with you so you can adjust your camera in the dark. The more images of the night sky you take, the more you will learn the best way to photograph them.