AstroPhotography Tips

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An intorduction to Wide Field Astro Photography (May 2004)

This month we look at where you can start with wide field imaging. This is particularly appropriate with the presence of comet C/2001 Q4 which is arguably best shot with wide field photography, not through a telescope.

Film or Digital? This will depend on what camera you currently own. Either are good for wide field photography however it may depend on the quality (and unfortunately cost) of your digital camera. Entry level digital SRL cameras provide excellent wide field results with exposure times of 30 seconds to 5 minutes. Film cameras with a fine grain can produce almost the same detail with arguably better colour and at a fraction of the cost. Point-and-shoot digital cameras are not very well suited but are worth giving it a shot if that is all you have.

What focal length? Again this will depend on what you own and also what astronomical target you are photographing. Start rails and Milky Way photography is often best with very wide angle lenses – 17mm to 35mm. Small subjects such as comet C/2001 Q4 are more suited to longer focal lengths of 50mm – 200m. However, remember if you are just starting out you are likely to produce better results with a wider angle lens (shorter focal length).

What exposure time? If you are mounting your camera on a fixed tripod (or convenient brick wall if that is all you have) then an exposure of up to 30 seconds with a 50mm or wider lens will not show noticeable star trailing. Longer than 30 seconds and you will have star trails due to the rotation of the earth. A longer exposure time will result in more comet detail. A typical exposure time for getting good tail detail from Q4 is 10 minutes at F/4 and 400ASA slide film. However you will be surprised what you can get in 30 seconds with fast film. For comet C/2001 Q4 you can try a tripod mounted shot at 30 seconds, a large F-stop (F/4 to F/2.8) and a focal length of about 100mm. See how you go and adjust the zoom and exposure time for best results.

What film speed? If you are working from a fixed tripod then the faster the film speed the better. There are some relatively fine grain 800ASA and 1600ASA films available from photography stores that are perfect. If you are working from a tracked platform (and so can do longer exposure times without star trails appearing) you can experiment with film speeds between 200ASA and 800ASA. If you are using a digital camera this is somewhat less critical as you may be able to easily change the simulated film speed as you take each photo.