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Old 05-06-2021, 08:07 AM
bluesilver (Peter)
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Join Date: Jul 2018
Location: Australia, Tasmania
Posts: 427
Working out best focal length for planetary imaging with a Dobsonian

I am not sure if i have got this posted in the correct section, so apologies if i have got it in the incorrect place.

So i am planning to do some planetary imaging with a Skywatcher 16" Dobsonian which has GOTO tracking.

I realize it might not be the best ideal scope for imaging with, but i think it will work ok for planetary imaging.
So i got the book Planetary Astronomy for a bit of a read and research http://planetary-astronomy.com/

It is a very well detailed book but the math's that they get involved with is where i get completely lost no matter how many times i try to re read to sort out what they are going on about.

I have a ASI224MC camera was was hoping i might be able to use this with the Dobsonian.

I am trying to work out the best imaging ratio or what size barlow or not barlow to use or what they refer to as the best focal length for planetary imaging.
In the book they mention that it is uncommon in Planetary Astronomy not to use a barlow for imaging the planets.

But no matter how i look at it even with the Astronomy .tools site https://astronomy.tools/calculators/ccd
It tells be that adding a barlow will make things less compatible.

From what i can see so far, the imaging camera is 3.75µm and the scope focal length is 1800mm which all works out to be 0.43 pixels.

Just not really sure what i am suppose to do with these numbers unfortunately.
Then in the book they talk about taking an image of the planet, then open up WinJupos to get an image size pixel of the planet to work out the correct focal length.
All very confusing for myself .

So i was hoping someone might be able to offer a bit of advise or some information to help me get on the right track here.

I have all the processing programs, just trying to get tings setup correctly if possible with this setup.
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