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Old 07-06-2016, 04:35 PM
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Atmos (Colin)
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Join Date: Aug 2011
Location: Melbourne
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Originally Posted by Camelopardalis View Post
But...but...but...why would anyone want to image at gain 0
As you increase the gain it does drop the read noise but the overall dynamic range drops with it. i.e. the read noise falls slower than the decrease in well depth.

Yes you can image at gain 300 with 1s exposures in Lum (gregbradley noted that it clipped the core of M51 even at 1s). Using a 3nm Ha filter, if you can drop the read noise to 0.6e- you need ~50s exposures (at F/5) to be RN limited but your well depth is so shallow that even at that exposure time you're clipping.

To give a bit of a comparison, at gain 0 (where the 1600 has its highest dynamic range) compared to a KAF-16803 on the same telescope, they need about the same exposure time to become RN limited. This is given that the KAF has a RN of 8e- (I believe that RickS mentioned a while back that this is what his PL16803 gets at SRO), this is within a margin of 10% (the 16803 reaches RN limited a fraction quicker without taking dark current into consideration but the 1600 is likely to be lower in that regard) . The 16803 has 5x the well depth however so while the 1600 will clip stars and bright cores (thinking of lagoon, M31, M42 ect) the 16803 will barely notice the difference.
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