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New Planetary Imaging Train - Can't Get Focus

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#1 Cloudy Planet

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Posted 28 February 2024 - 02:36 PM

The 1st photo is my planetary/lunar setup I’ve been using for a while on my Skywatcher 200p F5 - Imaging Source DMK41 AU mono camera, filter wheel and x3 Barlow.

 

It can be very difficult getting a planet on the small camera sensor so I invested in a Baader Flip Mirror II, together with a new Barlow, the Celestron X-CEL LX X3.

 

The 2nd photo shows my new setup with the flip mirror and new x3 Barlow - The new imaging train is about 25 mm longer than it was before.

 

Though now I cannot get focus anywhere near. All I can get of Jupiter is a big donut on the laptop screen, this is the case even through an eyepiece on the flip mirror.

 

This sounds like a back focus issue unless I’m mistaken. Does anyone have a solution to solve this problem?

 

Thanks

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#2 rblackadar

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Posted 28 February 2024 - 04:43 PM

Newtonians are tricky. They don't give you a lot of room to introduce elements upstream of the focal point, as you are attempting to do with the flip mirror. Basically, I think what's happening is that your focal plane is somewhere inside that unit, near the mirror surface, when the focuser is fully racked in. But that means you'll never get either your EP or your Barlowed camera to work.

 

One thing you could try is to move the Barlow upstream of the flip mirror, i.e. first element after the focuser. Certainly, the Barlow needs to come before the focal plane, so I think that's your only choice. (Eliminating the nosepiece attachment is another idea, i.e. screwing the mirror directly to the focuser somehow, but I don't think that will shorten it enough.) Moving the Barlow forward will increase its power, so that maybe a 3x won't be appropriate any more.



#3 kathyastro

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Posted 28 February 2024 - 04:50 PM

You have a long-ish adapter between the focuser and the flip mirror.  You might need to replace that with something shorter.



#4 Cloudy Planet

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Posted 28 February 2024 - 04:59 PM

Thanks rblackadar

 

… I'll try as you said, putting the Barlow first before the flip mirror, and give it a go on the next clear night.  
That makes sense now you explained where the focal plane likely is


Edited by Cloudy Planet, 28 February 2024 - 05:06 PM.


#5 Cloudy Planet

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Posted 28 February 2024 - 05:12 PM

Thanks Kathyastro,

 

That’s the original eyepiece holder that came as part of the telescope, it does screw out. 
But yes it’s another option I could look at replacing with something shorter




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