“My star trail images are made by taking a time exposure of about 10 to 15 minutes. However, with modern digital cameras, 30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures I do what many amateur astronomers do. I take multiple 30-second exposures, then ‘stack’ them using imaging software, thus producing the longer exposure.”
Thats my guess as well. What's weird though is that either the rotations are going much faster than I thought, or the long-exposure noise reduction or something similar is still turned on. (Without that, a camera can effectively immediately take another 30s exposure, so why the interruption otherwise?)
“My star trail images are made by taking a time exposure of about 10 to 15 minutes. However, with modern digital cameras, 30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures I do what many amateur astronomers do. I take multiple 30-second exposures, then ‘stack’ them using imaging software, thus producing the longer exposure.”
http://www.flickr.com/photos/nasa_jsc_photo/sets/72157629726...