Thread: Snr
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Old 24-10-2011, 02:24 PM
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pvelez (Pete)
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Join Date: Aug 2006
Location: Sydney
Posts: 1,250

I am working on an asteroid at the moment, trying to get a decent light curve. Its faint - about mag 15 - so I have increased my exposures and started guiding the shots.

Last night I had exposures 4 minutes long. My RC8 gives 0.68 arcseconds/pixel so I always bin - usually 2x2.

Now I understand that the higher the SNR the better for photometry and that SNR of 50 is ideal while sub-20 is troublesome.

My target varied over time - as you'd expect as it approached the meridian as the airmass decreased. The best I could manage was SNR of 21 and at lower altitudes it was down to around 12.

Here's the question - I had similar SNR at 3x3 and 4x4 binning. Should I expect better SNR at greater binning as I collect more light from my source? Or will the SNR only change as I increase the integration times? My experience is that a 4 minute shot at 3x3 is better than a 3 minute shot at 4x4.

I was calibrating with darks and flats. It was also a lousy night early in the evening with some cloud about.

Any thoughts?

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