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OAG Focus


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Hello

My first night out with my new OAG was an almost complete success! I set it up during the day and was happy everything was about right. Then pointed at the Crescent Nebula last night. I found some guide stars but struggled to get a good focus on them. I got the PHD2 HFD down to just under 5.5 but failed to get a sharp focus due to some out of collimation looking aberration thing.

Can anyone suggest a fix or a place to go to read up on OAG set up fine tuning please?

ZWO OAG
QHY5-iiM Guide camera
ASI294MC Pro Imaging Camera
9.25 SCT on a CGX
CPWI NINA PHD2

Thanks

Regards

Graeme

 

 

Screenshot 2022-07-01 231728.png

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Is that the best focus you got using the fine focus adjustment? Its not much adjustment from having seagull looking stars to round ones

I'd expand the box parameters on the guide star as you may lose the guide star quite frequently ( within the settings)

How well is the main scope collimated?

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30 minutes ago, newbie alert said:

Is that the best focus you got using the fine focus adjustment? Its not much adjustment from having seagull looking stars to round ones

I'd expand the box parameters on the guide star as you may lose the guide star quite frequently ( within the settings)

How well is the main scope collimated?

Hello NA

Yes, that's the best focus I could get. There is no fine focus adjustment, the main scope was focused accurately and then I focused the guide camera by moving it in and out manually whilst watching the PHD2 HFD figure. The main scope collimation was good. 

The OAG allows rotational movement to a few degrees and mirror height adjustment but I can't see any adjustment that would allow me to improve the quality of the guiding image other than adjusting the distance from the mirror to the guide camera sensor.

Would a mirror height adjustment make any difference? I didn't try that to avoid fiddling in the dark with an allan key!

 

 

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13 minutes ago, Graeme said:

Hello NA

Yes, that's the best focus I could get. There is no fine focus adjustment, the main scope was focused accurately and then I focused the guide camera by moving it in and out manually whilst watching the PHD2 HFD figure. The main scope collimation was good. 

The OAG allows rotational movement to a few degrees and mirror height adjustment but I can't see any adjustment that would allow me to improve the quality of the guiding image other than adjusting the distance from the mirror to the guide camera sensor.

Would a mirror height adjustment make any difference? I didn't try that to avoid fiddling in the dark with an allan key!

 

 

You found stars so it's low enough.. but I'd shoot some flats just to check that it's not too low and impeding into the light cone too much 

Yeah you can focus better pulling the camera in or out, but not much movement make alot of difference

PhD doesn't have an issue guiding on oblong stars but the better the focus is the better the snr

I use a 8 inch SCT and I think my hfd is a little lower , can't remember it in the 5's... Maybe  in the 3-4  area, so don't think you're  too far away 

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3 hours ago, newbie alert said:

You found stars so it's low enough.. but I'd shoot some flats just to check that it's not too low and impeding into the light cone too much 

Yeah you can focus better pulling the camera in or out, but not much movement make alot of difference

PhD doesn't have an issue guiding on oblong stars but the better the focus is the better the snr

I use a 8 inch SCT and I think my hfd is a little lower , can't remember it in the 5's... Maybe  in the 3-4  area, so don't think you're  too far away 

Well my flats showed no sign of the mirror at all so maybe I'll experiment with moving it a little closer in. I need to get it accurate so that the Stellarium ocular sensor frame is a true representation of what's going on.

And perhaps I just need to practice focusing the guide camera some more.

Thanks for your help.

Regards

Graeme

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44 minutes ago, Graeme said:

Well my flats showed no sign of the mirror at all so maybe I'll experiment with moving it a little closer in. I need to get it accurate so that the Stellarium ocular sensor frame is a true representation of what's going on.

And perhaps I just need to practice focusing the guide camera some more.

Thanks for your help.

Regards

Graeme

I've never had to rotate the guide cam to find stars .. I'm using a qhy 290

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Hi Graeme

Very similar star shape to my LodeStar on a 8" SCT with Full-Frame imaging.

Similar HFD, but stars nearest the bottom of the prism are best.

Obvious question is:

Do you have the prism adjacent to one of the long sides of the ASI294MC Pro sensor ?

And as Newbie said, lower the prism stalk until it just doesn't show on flats.

Michael

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55 minutes ago, michael8554 said:

Hi Graeme

Very similar star shape to my LodeStar on a 8" SCT with Full-Frame imaging.

Similar HFD, but stars nearest the bottom of the prism are best.

Obvious question is:

Do you have the prism adjacent to one of the long sides of the ASI294MC Pro sensor ?

And as Newbie said, lower the prism stalk until it just doesn't show on flats.

Michael

Cheers Michael

Yes, the mirror is on the long side of the sensor but it's a good few mm back from the edge. I'll move it in a bit to line it up with just short of the edge of the sensor and see if it shows on the flats. Just as soon as we get a clear sky here!

 

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