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Old 15-07-2017, 12:25 PM
brisen (Brian)
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SNR query on NB subs

I managed to capture some NB images last night on the central parts of the Lagoon Nebula and have run the subs through the Subframe Selector in Pixinsight. I am using an Atik 414EX with Baader NB filters on an ED120 and expected the SNR to be much lower then what is being reported by the measurement in PI.

The lights are 600 seconds captured at -10 C and the lowest SNR Weight that I got was 149.6 and it goes up to 171.5. Even a short 60 second H Beta sub is showing a SNR of 30.84 whilst the handful of luminance I captured initially, again 600 second subs, come in at 3.48 to 3.51.

I realise the whole Lagoon area is rich in HII, but am I missing something given that I was expecting the Ha subs to have much lower signal then the Luminance.

Brian
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Old 15-07-2017, 12:46 PM
JA
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Quote:
Originally Posted by brisen View Post
I managed to capture some NB images last night on the central parts of the Lagoon Nebula and have run the subs through the Subframe Selector in Pixinsight. I am using an Atik 414EX with Baader NB filters on an ED120 and expected the SNR to be much lower then what is being reported by the measurement in PI.

The lights are 600 seconds captured at -10 C and the lowest SNR Weight that I got was 149.6 and it goes up to 171.5. Even a short 60 second H Beta sub is showing a SNR of 30.84 whilst the handful of luminance I captured initially, again 600 second subs, come in at 3.48 to 3.51.

I realise the whole Lagoon area is rich in HII, but am I missing something given that I was expecting the Ha subs to have much lower signal then the Luminance.

Brian
Surely that can't be correct, IF the Signal to Noise ratio is indeed what is being measured! A Signal to Noise ratio of 3.5 would make for a very poor image. Are you sure there is not a 100x multiplier(or something) on that, or are the 3.5 SNR images noticeably vastly inferior to look at compared with the other images with the 170 odd SNR? If they look similar then I'd revisit the SNR calc.or sampling used in the software to see further to understand the discrepancy.

Best
JA
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Old 15-07-2017, 01:02 PM
brisen (Brian)
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Originally Posted by JA View Post
Surely that can't be correct, IF the Signal to Noise ratio is indeed what is being measured! A Signal to Noise ratio of 3.5 would make for a very poor image. Are you sure there is not a 100x multiplier(or something) on that, or are the 3.5 SNR images noticeably vastly inferior to look at compared with the other images with the 170 odd SNR? If they look similar then I'd revisit the SNR calc.or sampling used in the software to see further to understand the discrepancy.

Best
JA
Thanks JA. I just went back and looked at the L and the NB and the L is not that bad in comparison. I will do some more investigating with this once the weather clears here again.

Brian
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