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Getting focus on a 9x50 Skywatcher Finder for guiding

Astrophotography Beginner Equipment
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#1 SerApollyon

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Posted 07 March 2021 - 06:15 PM

Hello everyone!

 

This is my first post, so I apologize if I may be in the wrong category.

 

I am currently wanting to get into deep sky astrophotography, and I have all of my equipment together for it.

My setup consists of a Skywatcher EQM-35 Pro Goto mount,

a Skywatcher EvoStar ED 80/600 apochromatic refractor,

an Omegon 1200b M Mono guide camera,

a Sony A6000,

and all the necessary software for it (PHD2, APT, etc.) on a laptop.

 

Since the EvoStar ED80 already comes with a finder scope (the Skywatcher 9x50), I'd like to use it for guiding with my Omegon 1200b M, but my problem now is that I can't manage to get my Omegon close enough to the lens (and vice versa) to get stars into focus. Here you can see my PHD2, with the finder scope pointed at Denebola, completely out of focus:

unknown1.png

 

As you can see below, I already attempted to remove the screw ring to get the lens closer to the Omegon, but I still couldn't get it close enough.

unknown.png

 

My question now is if there's any sort of equipment (like, an extra lens or something) I could buy to get the stars into focus?

This may be a stupid take, but would an Omegon 0,5x Reducer help with the problem, since I was planning to get one anyway?

 

Thanks to anyone willing to help! Clear skies. smile.gif



#2 Blackhawk163

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Posted 07 March 2021 - 06:23 PM

Yes! I did this about a month ago, you're going to need a special adapter to make this work.
https://www.firstlig...-c-adapter.html

Go there. I had used this as my setup but I eventually went over board and am now using a redcat51 as my guide scope.

Good luck!

 

Franken guide scope

 


Edited by Blackhawk163, 07 March 2021 - 06:30 PM.


#3 barbarosa

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Posted 07 March 2021 - 06:45 PM

The female threads on the rear of most Synta focusers are standard SCT.

 

If you have a right angle Synta finder the conversion is relatively easy. I used an SCT to T 2 adapter and a T2 extension to position the sensor the camera sensor at the focal plane.

 

The measured distance from the rear flange of the objective cell to the sensor is about 150mm.

 

This might be approximately correct for all 50mm Synta focusers in recent years

 

Straight through finders are more of a challenge because of the longer tube. I was not able to find a suitable adapter and so never converted any of the straight through finders. But I've seen some solutions, including cutting the tube and some DIY adapters. No knowledge of how well they work.


Edited by barbarosa, 07 March 2021 - 06:47 PM.


#4 Andynator

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Posted 07 March 2021 - 07:02 PM

You're moving the wrong direction - you need more length, not less. The camera sensor should end up roughly in the same place as the eyepiece was.

#5 SerApollyon

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Posted 08 March 2021 - 12:37 AM

You're moving the wrong direction - you need more length, not less. The camera sensor should end up roughly in the same place as the eyepiece was.


I mean I tried it, but the further I moved it out the blurrier it got.

#6 SerApollyon

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Posted 08 March 2021 - 12:40 AM

Yes! I did this about a month ago, you're going to need a special adapter to make this work.
https://www.firstlig...-c-adapter.html

Go there. I had used this as my setup but I eventually went over board and am now using a redcat51 as my guide scope.

Good luck!


Thank you for the quick reply!

I currently have my camera attached with a T-Optics adapter and an Omegon T2 to 1.25" adapter (https://www.omegon.e...iblich-/p,33232).

Since I feel like my camera is almost as far in as it can be, I'm guessing with the adapter you linked I can manage to close the needed gap to focus?

#7 SerApollyon

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Posted 08 March 2021 - 09:53 AM

Okay, update: I ordered myself an Omegon guidescope today, that way I can be absolutely sure I shouldn't run into any problems guiding.

If I'm gonna do it, might as well use the equipment made for it. smile.gif

 

Thanks nonetheless for the help though!


Edited by SerApollyon, 08 March 2021 - 10:26 AM.


#8 barbarosa

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Posted 08 March 2021 - 12:55 PM

This appears to be  similar to the SCT Male to T-2 male adapter I used to convert a SW finder.

 

You're moving the wrong direction - you need more length, not less. The camera sensor should end up roughly in the same place as the eyepiece was.

 

The factory eyepiece focal plane sits very near to the back of the tube on the straight through finder scopes. Thus you cannot get focus by moving the camera farther away from the objective. Depending on the sensor recess distance you can get close to focus by bringing the camera right up to the end of the tube.

 

I see in older posts people saying the that 50mm Celestron finder scope has female 48mm threads at the back. All I can say it that none of the several Celestron and Skywatcher 50mm straight though finders I've seen were other than SCT threaded. There are also different numbers suggested for focal distance. I suspect that is a measurement or internet lookup difference and not an actual difference. But it could be that as the source of some of these parts changed from Japan to Taiwan or China there were also changes in the specifications.




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