“Rain” – noise to cause sleepless nights

Blog the previous nights viewing. Link to images on the gallery or simply describe what you observed the night before. Leave the technical and howto in another forum.
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DRatledge
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“Rain” – noise to cause sleepless nights

#1 Post by DRatledge » Sun Apr 14, 2013 10:06 am

At the recent imaging tutorial Gerald mentioned the dreaded “rain” noise. This is what it looks like. It is usually caused by differential flexure in guiding. You may think that as long as the tracking or guiding is good enough for each 5 minute exposures then everything will be ok. Not so - if over the course of taking a set of exposures, say 2 hours, there is a continuing drift then this will manifest itself as noise in the image that looks like rain – diagonal streaks all across the image. This is virtually impossible to remove. Guidescopes have to be very rigidly attached to avoid it. This recent image of mine resulted from a computer lock-up interrupting guiding. On seeing the result it was 2 days before I could get a decent night’s sleep!.
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