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Could not find guide star with the Celestron OAG and the ZWO ASI 220mm mini camera

ZWO ASI290MM Mini ZWO ASI220MM Mini Acquisition Guiding Deep Sky
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Jerry Gerber avatar
Jerry Gerber avatar
Tonight I was using the Celestron Edge 8 with the Celestron OAG.  I simply could not find a single guide star while looping, I didn't even get as far as calibrating because no guide stars were showing up in ASIAIR Plus.  I tried swapping the ASI 220mm mini with the ASI 290mm mini but that camera also could not find any stars.  I tried changing the gain multiple times, changing the exposure time and rotating the OAG into different positions.   I was working at 1422mm FL using the Celestron .7 reducer.  My focusing was very precise as I was using an electronic focuser.  Sky was clear, no clouds, moon below horizon, Bortle 7 skies. 

Any tips as to finding guide stars?  I'll have to check the prism position in OAG but I think it's in the right position, not too low or too high.

Thanks!
Jerry
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Rob Johnson avatar
Rob Johnson avatar
I’ve had this once or twice with my setup under Bortle 7, 12” f5 Newtonian and OAG with QHY5LIIM guide camera, has happened away from the plane of the Milky Way with few stars. The only solution I could come up with was to extend the exposure time to as much as 8 seconds until a faint star was detected, certainly not ideal and lost more frames due to elongated stars. In future I would move the field a little to try and get a brighter star. The downside of OAG’s 😕

Rob
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Andrea Girones avatar
Andrea Girones avatar
You could also try Bin2 for a guide star. There is a video out there on using the OAG and stellarium and entiering the OAG details so you can plan in advance to see if there are suitable guidestars or not. good luck
Scott Badger avatar
Scott Badger avatar
Not sure if any of this applies to your situation Jerry, but I have a 9.25 edge plus ZWO OAG and spent most of last winter not finding guide stars. I chalked it up to the common complaint about OAG's, made worse by my dropping the reducer and going to the full FL (2350mm) plus the poor seeing at my location which gets even worse during the winter. Finally I got frustrated enough that I decided to push the stem/prism of the OAG further into the light stream even if it meant showing up in my images and needing to be cropped. In the process I discovered two incorrect assumptions. First that I couldn't go any further in with the prism without impacting my images, but it turned out that I still had more margin to work with, and second that my OAG was properly focused in the first place. It had been focused, and not sure what might of led to its losing focus, but poor focus was probably more of an issue than the prism placement.  I was assuming poor focus would show fat stars, not no stars, but after pushing the prism in a bit, I decided to refocus the guide camera for good measure even though the new prism placement shouldn't require it. Suddenly, I went from 1 or 2 stars in the fov, if I was lucky, to at least a few and usually many. FWIW.

Cheers,
Scott
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Kelly Wood avatar
Kelly Wood avatar
I use that exact setup except with the 174mm guide camera and can confirm: poor focus on the OAG can mean you see no stars at all. If you can confirm OAG focus in another patch of sky and all looks fine, then you may just be in an unlucky spot for that focal length. If you can't find stars *anywhere* you point the scope, then I'd suspect either focus issues or the prism is not far enough into the optical train. You can actually go pretty far in before it starts impacting your images. Slight impacts on the outer edge of one side of the image can also mostly be taken care of with good flats.

Good luck. I found using an OAG was the absolute key to good guiding at that focal length.

-Kelly
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Jerry Gerber avatar
Jerry Gerber avatar
Well, this has got to be one of the dumbest mistakes I've made so far in astrophotography! 
The OAG was backwards!  The prism was facing the opposite direction because when I put the two adapters on it, I put each one on the wrong side. 
No wonder there was no image in the prism!!

That's fixed, so on the next clear night (probably in 1 month to 6 months from today) I'll see if any other OAG issues come up. Hopefully that will be the end of it and I can start imaging…

Thanks to all who replied to my post!

Jerry
www.jerrygerber.com
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
Jerry Gerber:
Well, this has got to be one of the dumbest mistakes I've made so far in astrophotography! 
The OAG was backwards!  The prism was facing the opposite direction because when I put the two adapters on it, I put each one on the wrong side. 
No wonder there was no image in the prism!!

That's fixed, so on the next clear night (probably in 1 month to 6 months from today) I'll see if any other OAG issues come up. Hopefully that will be the end of it and I can start imaging...

Thanks to all who replied to my post!

Jerry
www.jerrygerber.com

We've all been there! Glad it was figured out. Now I will add this to my list of troubleshooting questions.
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Scott Badger avatar
Scott Badger avatar
Ha! Well, one time I was stumped a lot longer than I want to admit trying to figure out why I wasn't seeing any guide stars…..then finally looked up and saw the cloud.

Cheers,
Scott
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Jure Menart avatar
Jure Menart avatar
Jerry Gerber:
Well, this has got to be one of the dumbest mistakes I've made so far in astrophotography! 
The OAG was backwards!  The prism was facing the opposite direction because when I put the two adapters on it, I put each one on the wrong side. 
No wonder there was no image in the prism!!

That's fixed, so on the next clear night (probably in 1 month to 6 months from today) I'll see if any other OAG issues come up. Hopefully that will be the end of it and I can start imaging...

Thanks to all who replied to my post!

Jerry
www.jerrygerber.com

Great to hear you sorted it out! And kudos to be honest, it's good to hear it's not only me doing stupid mistakes

I'd suggest you try to focus full setup during the day. You can easily point it to far away target (I am using forest on small hill nearby) and it's quiet easy to focus both. I also trained myself during the day how to fine tune (slide the camera up and down slightly to fine tune focus ) it at the start of night session.

BTW I have similar setup - C8 (2032mm FL) + 0.7 focal reducer.

CS,
Jure
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