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Nyquist Sampling Theory & Implications To Solar

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#1 marktownley

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Posted 21 January 2013 - 02:48 PM

Hi there,

I wrote an article on my website discussing Nyquist sampling theory, oversampling, undersampling and it's implications to solar astronomy. The link is here >>>

http://brierleyhills...theory-under...

I would welcome any thoughts, discussion, experiences any of you would like to share.

Thanks,

mark :)

#2 BYoesle

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Posted 21 January 2013 - 11:33 PM

An excellent piece Mark! Thorough and a something to consider - especially for when the seeing will allow theory to be approached. Thanks! :waytogo:

#3 DavidM

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Posted 22 January 2013 - 10:09 AM

Thanks for that Mark. Very interesting. I ran the numbers on the 152 (900mm focal length) and my camera, and the minimum Barlow I should be using to not undersample is 2.4x, which seems about right to me as I use a 2.5x powermate by default and reckon I could push it to 3 or 3.5x on a good day (though I suspect such days will be rare here in Perth). When I had really good seeing in Oman I could use the 3.5x barlow on the same scope for CaK and that seemed about as far as I could ever expect to go given the susceptibility of that wavelength to poor seeing.

#4 Andy Devey

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Posted 22 January 2013 - 02:18 PM

Hi Mark, extremely interesting, this also means that the newer high speed cameras with smaller pixel sizes drive down the optimum focal length so not really suitable when attempting for higher resolution long focal length imaging?

Regards

Andy

#5 marktownley

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Posted 24 January 2013 - 02:24 AM

Hi Mark, extremely interesting, this also means that the newer high speed cameras with smaller pixel sizes drive down the optimum focal length so not really suitable when attempting for higher resolution long focal length imaging?

Regards

Andy


Hi Andy, that's one way of looking at them I guess! Another way i've looked at this from is that these smaller pixel cams are (potentially) better suited to CaK than Ha wavelengths...

#6 marktownley

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Posted 24 January 2013 - 02:27 AM

Thanks for that Mark. Very interesting. I ran the numbers on the 152 (900mm focal length) and my camera, and the minimum Barlow I should be using to not undersample is 2.4x, which seems about right to me as I use a 2.5x powermate by default and reckon I could push it to 3 or 3.5x on a good day (though I suspect such days will be rare here in Perth). When I had really good seeing in Oman I could use the 3.5x barlow on the same scope for CaK and that seemed about as far as I could ever expect to go given the susceptibility of that wavelength to poor seeing.


Hi david! :)

Quite a few people havbe said that they often by default arrive at the numbers for f.l. for Ha that this predicts, but rarely with CaK due to poor seeing. Interesting stuff!

Thank you also Bob!

mark :)

#7 dbowlin

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Posted 26 January 2013 - 10:00 AM

Thanks Mark, great food for thought. I just ordered a new PGR Chameleon, thanks to Bobs posting on another thread. I ran the numbers for my Solarmax II 60 and I will use my 1.6 Barlow to get close to optimum. Should be fun, if not I can blame Bob. LoL
Dale

#8 marktownley

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Posted 27 January 2013 - 03:38 AM

Hi Dale, I think you will find the 1.6x barlow works very nicely with that scope :)

#9 Spectral Joe

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Posted 28 January 2013 - 12:04 AM

Mark

Thank you, keep bringing on the math and science.

Joe






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