Quote:
Originally Posted by jase
Deviating OT here, but for CCD work, longer subs are the only way to go. As I mentioned in a previous post, the signal to noise ratio of a CCD increases linearly with the square root of the exposure time. This means that quadrupling the exposure time doubles the signal to noise ratio. So take the longest effective exposure you can. This applies to all forms of CCD imaging, but is especially important for narrowband imaging where filters restricted the quantity of light reaching the chip.
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This is true but I find I get to a stage of diminishing returns. The problem is time available vs usable pics. As the exposures get very long in my camera the stars saturate and bloom. This degrades the images more than the readout noise.
There is an interesting article about this at
http://www.licha.de/astro_article_ccd_combining.php