Moving Pictures

Tony Flanders
In the August 2009 issue of Sky & Telescope, we describe how to make time-lapse movies of the night sky from individual frames shot with a DSLR. Several practical problems have to be overcome first. First of all, what exposure times and f-stops should you use? Click here to download a table in Excel format showing some values that have worked well for us.

One constraint on movie making is the storage capacity of the memory card where the images are being stored. Fortunately, this is less of an issue than it used to be with today's big, cheap, memory cards. Here are some guidelines for how long you can expect to keep shooting at a rate of one frame every 30 seconds:

Typical Image Sizes for an 8 Megapixel Canon EOS 350D
Quality Size (Mb) Images (2 Gb card) Hours (30 s exposures)
Raw 7 289 2.4
Large Hi 3 675 5.6
Large Low 1 2024 16.9
Mid Hi 0.8 2530 21.1
Mid Low 0.6 3373 28.1
Small Hi 0.4 5060 42.2
Small Low 0.2 10120 84.3