Simple Whole Sky Imaging

I personally find that taking images of the night sky is a rewarding past time. The simplicity of the technique is what really makes it enjoyable. With modern consumer digital cameras anybody can take stunning sky vista photographs. The only requirement is that the digital camera have a manual setting which allows control of the settings and is able to take long exposure 30s and greater. Most digital cameras people own these days can easily do this and the result will be pleasing photos of the night sky and no extra cost — all that is needed just dark skies.

Figure 1: Auriga Full Sky Image 30s Exposure with a Cannon Xsi

Such images provide a simple method for extending you views of the night sky with the milky way being visible in a 30s image in most cameras.

The key here is to not expect too much; if you’re skies suffer light pollution, this will fog out the camera really quickly and you will loose any real definition of the sky. The main point is to keep it simple. The issue of light pollution is a key problem here as not only will the camera detect the sky objects but it will also detect all of the skyglow caused by bad street lights or over lit shopping malls. mitigating this will be the subject of another page later. In general thought if you only want to take pictures of the night sky and the you can see the objects with the naked eye then take a digital camera with a long exposure should work.

So how easy is simple?

There is no hidden art in this type of astrophotography. The key equipment is a camera which is capable of long exposures. In this case it does not even need to be digital, if you have a 35 mm film camera this will work just fine. I would recommend the use of a slide film with an ISO of 400 to 800 and when it comes to have the film processed ensure that you ask them not to cut the film negatives as automated processing will fail to detect the images of stars and or ask to have the slides mounted which will be cut correctly and mounted as this is generally a manual process. Unfortunately the amount and availability of film for cameras is dwindling these days so the if you looking for a camera to take this sort of photo then digital is the way forward.

With the plethora of digital cameras it is likely that most people will already have a camera which is capable of this form of photography. One of the great advantages of the digital cameras is the speed at which you will be able to see your masterpiece or be able to quickly delete the photo as its just not right…. Most digital cameras now are more sensitive that their film counterpart and this is important as you can detect more photons in a shorter time which means that the star trails will be minimised (see below).

Wether you use a digital camera  or a film based one the process for capturing sky images is the same: mount camera on tripod (optional I have used tree stumps and car roofs but the tripod really makes it simple!) focus camera on infinity and shoot. This is really all that it takes. once you have mastered the simple picture then its time to look at the different camera settings and start to play with them.

A camera which has a full manual mode will allow the user to change the focal ratio of the lens i.e. f-number. it is recommended to have this set as short as possible as this means that the most  light is getting into the camera. I normally use f4.5 as this is what is set on my camera. the only other setting to really be concerned about is the ISO number. The higher the number the most gain the CCD chip has but also the noisier the image will be. if at all possible i shoot at ISO800 on my Cannon XSi but the latest cameras have ISO setting which are much higher i.e. 6400 and with better noise profiles. once i have these settings i will take a series of 30 second exposures

So what can you type of phenomena can you photograph this way?

  1. Eclipses — maybe better with a telescope but the wide field views from cameras in my view are much better than telescopic views.
  2. Constellations — great way to learn the night sky. in the image to the right can you see a number of different constellations?
  3. Satellites
  4. Aurora Borealis — also one of my favorites

So what are the pit falls ?

  1. Well the earth is rotating so the maximum exposure that you will be able to take is probably about 1 minute without seeing star trails — but these are good sometimes.
  2. Any moon or other sky glow will severely hinder the picture. Longer focal lengths can flatten the skyglow but this then requires longer exposures.
  3. The field of view can be very large and the number of stars visible can make it difficult to find the objects which were being imaged

Taking pictures this way is simple and easy. It only requires equipment which most people already own and the pictures are simple to process and enjoy.

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