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Planetary imaging rule of thumb help.

astrophotography CMOS imaging planet reflector
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#1 Astro Joshua

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Posted 24 November 2020 - 05:01 PM

Hey so I’m looking to get into planetary imaging with my 8 inch f/5.9 dobsonian. I have been looking at the asi120mc-s(I know the asi224mc is better but a little out of my budget currently). The camera has a 3.75 pixel size. The rule of thumb being 3.75 x 5 = f/18.75. I already own a 2x Barlow would this work ok or do I need to get a 3x Barlow to get closer to the f/18.75?

Also I’ve entered these things into stellarium to see what kind of views to expect and it’s higher than the 400x max magnification my telescope gets. Does the max magnification still apply when imaging or not? I’m looking to put my order in on Black Friday so any replies before then are appreciated. Thanks! 



#2 Tulloch

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Posted 24 November 2020 - 05:05 PM

Hi there, here is an explanation of the rule of thumb using maths. You will get a little more magnification from the 2x Barlow when you image, so you will be close. If you are not guiding, then centering the planet will not be easy, so it might be worth sticking with the 2x for now.

 

Hope this helps,

 

Andrew

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  • Maths for f-number = 5x pixel size.jpg

Edited by Tulloch, 24 November 2020 - 05:06 PM.


#3 Astro Joshua

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Posted 24 November 2020 - 05:18 PM

Ok thanks. I’ll be using the undriven/image drift method so we’ll see how it goes. 



#4 RedLionNJ

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Posted 25 November 2020 - 12:51 PM

I was waiting for Andrew to post the mathematical explanation - thanks :)

 

On top of this, bear in mind the seeing will very, very rarely permit you to get the best out of the full f/18.  You're totally fine around f/12 most of the time.  If you do manage to get excellent seeing, you can use AutoStakkert's 1.5x drizzle feature to being out any finer detail which was recorded.


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#5 Tulloch

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Posted 25 November 2020 - 03:13 PM

I was waiting for Andrew to post the mathematical explanation - thanks smile.gif

It's not my image Grant - feel free to repost it yourself :). FYI, it comes from here...

https://www.cloudyni...w/#entry5317455




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