Light from the Dark – Stellar night Photography

There is a lot to be said about stellar night photography, but let’s start with the basics. Presumably you are equipped with a Digital Single Lens Reflex (DSLR). The reason for selecting a DSLR camera is that what you see through the viewfinder is shared with the imaging sensor. What You See Is What You Get (WYSIWYG) as they say in the computer business.

Next, you have to decide on your type of shot. What do you want in the final image? Star trails, pinpoint stars, foreground enhancement? Each choice will change your technique.

Finally you’ll have to obtain some basic equipment:

  1. A good solid tripod, especially if it is a bit windy
  2. Something to keep your lens from fogging up (cloth wrap and elastic bands work)
  3. Fully charged batteries, as long exposures are draining, or somewhere to plug in
  4. A hat and thermos of hot drink
  5. A remote trigger for the camera (radio, infrared or squeeze bulb)
  6. A Star Chart to find your target
  7. MP3 player or book to fill the time during long exposures

Steady Pinpoint Stars

This is accomplished in two different ways. You can use a motorized equatorial mount, such as that found on a telescope, to lock your camera to the sky for an extremely long exposure time. This is ideal for fainter objects, like distant galaxies, or even our galactic core (The Milky Way) where a black hole happens to live (though by definition you can’t photograph a black hole since it emits no light). This is particularly true if you have nothing in the foreground, or if you don’t mind a surrounding blur of foreground objects.

In truth, it is the only way you’re going to get a good photo of a comet or nebula. The most important thing here is to turn on the camera’s Long Exposure Noise Reduction feature. This is actually related to Quantum Physics in how “static” or spurious pixel stimulation occurs and can severely mess up your image.

If you don’t have this feature, you can try your camera to see how well it performs. Excessive “noise” might make it very hard to obtain high quality images. Your stellar picture career might require an upgrade in camera.

Or…

The second way is by using the Rule of 600 which takes into consideration that the sky travels 360° per day and a typical 24mm lens has about 75° field of view. Without getting needlessly detailed and making you do math, a 24 Megapixel camera can keep its aperture open for about 20-25 seconds before the star moves enough to stimulate more pixels and cause a blur or “trail”. This is with the widest possible aperture and your ISO set high enough to obtain a good exposure.

To find your exposure time divide 600 by the focal length (600/24= 25 seconds) and that will tell you how long you can expose before you lose the “pinpoint” effect. A lens with a 300mm focal length could thus be exposed for two seconds (600/300) before blurring occurs.

Field of View & Shooting in the RAW

It is important to remember that if you are photographing Polaris it is almost motionless in the sky, so a tight close up of a small patch of sky there will show far less motion than if you were looking at the Great Square of Pegasus, which would show substantial motion (being so far off the celestial axis). If you’re going to take multiple shots and then stack them, shoot in RAW mode so they are easy to manipulate in software. There is freeware for this purpose available here. Stacking allows you to get much more detail by adding all the collected light from several short shots, rendering much brighter stars and much fainter objects. Remember to leave a blank frame between series of images so you can tell them apart later.

Star Trails

On the other hand, some very attractive picture compositions have been created by deliberately engendering star trails. In this case you can still use your widest aperture, but it will be necessary to turn your ISO down to 100 or minimum, so as not to over expose.

Start with a five minute exposure, and then double it for the next one, and keep adding increments of five minutes until you get a satisfactory image. Putting Polaris in a top corner often renders an attractive image, but dead center is also a favorite choice.

Foreground

Consider using an object in the foreground for a silhouette, or if you have created a beautiful starry background, use a flashlight (quickly) to illuminate the foreground object (keep it moving to avoid “hotspots”). Or you can even try a flash if you want it stark. Various gels (filters) on your flash can give a nice general coloration to trees or cliffs. A body of still water can be an excellent reflector for your sky image!

Conclusion

Ultimately it comes down to experimentation. You’ll have to find what satisfies you personally. Get out there and be our next Ansel Adams!

No Comments

    Leave a reply