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Old 02-07-2017, 02:04 PM
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RickS (Rick)
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Quote:
Originally Posted by alpal View Post
Yes - I think the article I pointed to below is a rebuttal
of Nyquist's sampling theorem that we've all been using.
3 x is considered better than twice when considering sampling.
There's nothing wrong with Nyquist sampling at 2x but the conventional use (sampling a single analog signal) isn't what we're doing.

Stan Moore makes a pretty good case that you should sample at about 3.5x for imaging: http://www.stanmooreastro.com/pixel_size.htm

Quote:
Originally Posted by Slawomir View Post
I'm wondering if purposely putting together a system that reasonably under-samples and then drizzling data is the ultimate solution for amateur astrophotographer.
That's what we're doing with the C300 at SRO (image scale 1.26 arcsec/pixel with seeing often down to 1 arcsec) and what I had in mind when I matched the AP140EDF with 9um pixels (2.4 arcsec/pixel with typical poor SEQ seeing.)

I like this approach because it gives you better resolution than the image scale, a big FOV and images that you can print really big.

Quote:
Originally Posted by Slawomir View Post
As I understand it, at the same f-ratio (and same QE+read noise), undersampling system will be going deeper in the same time as opposed to a well-sampling system (say 2"pp at f/6 vs 1"pp at f/6), thus in the end one will have a higher SNR and a similar detail with undersampled and drizzled data comparing to a well-sampled data, given equal time of exposure. Or am I missing something here?
Alas, it's not magic, Suavi. The increase in resolution does come at the expected cost in reduced real SNR. It's just that the apparent SNR is better because of the way that Drizzle correlates noise. It effectively does noise reduction. You can get the same effect by applying noise reduction to the data from a well-sampled system.

Cheers,
Rick.
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