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Off axis guider setup!

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#1 Angel baby

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Posted 27 February 2024 - 12:29 PM

Hello this may be the. wrong area, sorry if it is.

My problem is that in trying to set up my zwo off axis guider I focus the main camera then switch over to the oag (guide camera) but I get a different thing to focus on, the main camera is focused on a tv aerial but the oag is on plants in my garden which are just below the tv aerial. Although both images are coming through the same scope, why? The only thing I can think of is the prism on the oag, I’ve moved it up but maybe not far enough. Anyone help please.



#2 DirtyRod

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Posted 27 February 2024 - 12:37 PM

Depending on the focal length, the two may not have perfect alignment. The prism could be slightly off or it might be the fact that your guide scope is looking down the edge of the FOV versus the center. 

 

That all said, they do not have to be in perfect alignment to guide well. Most likely they won't be when you do your final focus on stars that are much further away. 



#3 Angel baby

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Posted 27 February 2024 - 12:59 PM

Hi, my scope is a Sharpstar 94 edph. I don’t have a guide scope attached as I’m using, or trying to, an off axis guider which is a mistery in as much as the main camera is focussed on a tv aerial and when I switch over to the oag it’s looking somewhere other than the tv aerial. I can’t fathom this out as both cameras are looking down the same scope. Why do you think they are on different targets?



#4 Dino

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Posted 27 February 2024 - 02:38 PM

The two cameras are looking down the same scope, but they image different areas of the field of view of that scope, so you see different things in the images of these two cameras. All is well! If the OAG camera would show the same or even part of the same image as the main camera it would cast a shadow on the main camera, something you do not want. The field of view of the two cameras is different, just as it’s supposed to be.


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#5 Angel baby

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Posted 27 February 2024 - 02:52 PM

Thanks I feel better now. After some days trying to focus things it’s good to know I’m getting there. Just need a clear night to test things out.



#6 jdupton

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Posted 27 February 2024 - 03:00 PM

Angel baby,

 

Hello this may be the. wrong area, sorry if it is.

My problem is that in trying to set up my zwo off axis guider I focus the main camera then switch over to the oag (guide camera) but I get a different thing to focus on, the main camera is focused on a tv aerial but the oag is on plants in my garden which are just below the tv aerial. Although both images are coming through the same scope, why? The only thing I can think of is the prism on the oag, I’ve moved it up but maybe not far enough. Anyone help please.

   Both cameras are looking at the same filed of view from the telescope but each is looking at a different portion of the whole field. See the illustration below using M45 as a target.

 

FOV_with OAG.png

 

   The larger main circle is the full field of view that the telescope may produce at the image plane. Your main camera is On-Axis and is represented by the rectagle at the center of the round full field of view. Stars within that area are what show in the main camera. Your guide camera is Off-Axis and is represented by the smaller rectangle above the center. Only stars in that rectangle show up in the guide camera images. Each sees a different portion of the full field produced by the telescope. Since each camera sensor is looking at a different area within the whole field, they see different views. 

 

 

John


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#7 DirtyRod

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Posted 27 February 2024 - 05:09 PM

Hi, my scope is a Sharpstar 94 edph. I don’t have a guide scope attached as I’m using, or trying to, an off axis guider which is a mistery in as much as the main camera is focussed on a tv aerial and when I switch over to the oag it’s looking somewhere other than the tv aerial. I can’t fathom this out as both cameras are looking down the same scope. Why do you think they are on different targets?

Understood that you are using the OAG. I probably should have said OTA. The imaging camera looks down the center of the OTA and the prism of the OAG picks up the light from the side of the OTA as John illustrated. 

I assume you know that getting them focused during the daytime is a good start but that focus at night on the stars will be different and require you to refocus both cameras. 



#8 Angel baby

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Posted 27 February 2024 - 05:30 PM

Thanks guys. If only someone would put together a video that starts at the beginning, I.e attaching the oag to a scope, then the setting's in your ASIAIR if you are using one or settings for what ever you use for image capture,then what to expect once you’ve managed to focus both cameras. Basically filling in the gaps that seem to be overlooked, especially for dumb nuts like me.



#9 Angel baby

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Posted 29 February 2024 - 09:49 AM

Hi, I can’t edit my previous post and I have another question, where do I connect the oag camera? To the back of my zwo2600 mm camera which is the main camera or to the ASIAIR plus.



#10 DirtyRod

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Posted 01 March 2024 - 12:01 AM

Hi, I can’t edit my previous post and I have another question, where do I connect the oag camera? To the back of my zwo2600 mm camera which is the main camera or to the ASIAIR plus.

Either will work.



#11 descott12

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Posted 01 March 2024 - 12:03 AM

Not sure if it was mentioned above but I am just now setting mine up as well. Having a big target to focus on helps. I just used the full moon and it made it easy to get both cameras focused.



#12 Angel baby

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Posted 01 March 2024 - 05:30 AM

Clear sky would help. I have not seen either the Moon or stars for ages.



#13 F-Astro

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Posted 17 March 2024 - 05:51 PM

Hi Angel,

 

If the TV aerial and your garden plants are both in focus, but they are not at the same distance from your scope, you might want to check out my thread linked below. I likewise just switched to an OAG and had focus issues.

 

https://www.cloudyni...i-missing-here/

 

CS, 

Fran




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