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How do folks focus their guide scopes?

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13 replies to this topic

#1 sternenhimmel

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Posted 14 April 2024 - 08:24 PM

Mains scope focus is easy now that I have an EAF, but even before I could use the Bahtinov mask to dial it in manually. For the guide scope, I sort of just make adjustments and squint to see if the stars look sharp enough or not. Should I just get a 30mm Bahtinov mask, or is close enough good enough? 


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#2 brlasy1

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Posted 14 April 2024 - 08:34 PM

Mains scope focus is easy now that I have an EAF, but even before I could use the Bahtinov mask to dial it in manually. For the guide scope, I sort of just make adjustments and squint to see if the stars look sharp enough or not. Should I just get a 30mm Bahtinov mask, or is close enough good enough? 

I purchased a Bahtinov mask for my guide scope.  You could also use the moon while it's cycling. 



#3 afd33

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Posted 14 April 2024 - 08:35 PM

Close is good enough. Granted this was with an OAG, but before I got everything figured out on my C8 my guide stars looked like crescents and it guided well. When I used a guide scope, I focused it one time, and I didn't touch it for the two years I used it since I was able to keep it all together all the time.



#4 shakafell

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Posted 14 April 2024 - 09:36 PM

Its preferable for guide stars to be slightly out of focus so there is no need for exactness.


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#5 archiebald

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Posted 14 April 2024 - 09:41 PM

With my previous guide scope and even now with my OAG, I focus on a distant comm tower during daylight.

 

In EKOS I set the camera to take looping exposures while dialling it in.



#6 bobzeq25

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Posted 14 April 2024 - 10:10 PM

Mains scope focus is easy now that I have an EAF, but even before I could use the Bahtinov mask to dial it in manually. For the guide scope, I sort of just make adjustments and squint to see if the stars look sharp enough or not. Should I just get a 30mm Bahtinov mask, or is close enough good enough? 

I minimize the guidestar width in PhD2.  Easy and effective.  Is adjusting exactly what is important to adjust.

 

Another (inferior) possibility is to look at the guide field in PhD2, and maximize visibility of dim stars (even if you're not using them for guiding).


Edited by bobzeq25, 14 April 2024 - 10:12 PM.

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#7 arbit

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Posted 14 April 2024 - 10:35 PM

Depends on 2 things - mount and seeing.

If its a strainwave mount then good focus does help. Guidescopes are usually very fast, so the critical focus zone is quite small, and it's easy to be wildly off.

You can get good focus through Bahtinov, PHD2 fwhm, or number of stars visible in PHD2.

If the seeing is bad (like mine recently), the fwhm jumps around too much frame to frame, so a Bahtinov works better.

You may not be able to use the software for Bahtinovs as the spikes in small scopes may not be recognised, but visual should be fine especially if using multistar.

Sent from my SM-S908E using Tapatalk

Edited by arbit, 14 April 2024 - 10:36 PM.


#8 acrh2

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Posted 14 April 2024 - 10:44 PM

Its preferable for guide stars to be slightly out of focus so there is no need for exactness.

No longer true with modern hardware.

 

https://www.cloudyni...post&p=13367186


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#9 Fegato

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Posted 15 April 2024 - 02:17 AM

I use the Sharpcap multi-star focus routine - nice and easy to get it well focused. I also use Sharpcap for polar aligning. Both work well for me.



#10 TelescopeGreg

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Posted 15 April 2024 - 10:01 PM

I focused for maximum number of tiny stars as seen in a regular imaging app (not PHD2).   It's amazing how they pop into view when your focus is good.


Edited by TelescopeGreg, 15 April 2024 - 10:02 PM.

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#11 Oort Cloud

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Posted 16 April 2024 - 11:45 AM

I just use the star profile in PHD2, while looping short exposures of 0.5-1.0s. If the star stops getting smaller and starts getting larger, I undo the last adjustment and lock it down.

There is a small amount of lag in the system, so I generally wait about 2s after each adjustment before noting the FWHM reading.

#12 DanMiller

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Posted 16 April 2024 - 12:45 PM

Mains scope focus is easy now that I have an EAF, but even before I could use the Bahtinov mask to dial it in manually. For the guide scope, I sort of just make adjustments and squint to see if the stars look sharp enough or not. Should I just get a 30mm Bahtinov mask, or is close enough good enough? 

Honestly, I used N.I.N.A. to focus mine in.  Instead of connecting to my main camera, I connected to my guide camera. Then went to the image tab and took images while I adjusted the focus to get a reasonable HFR. It just was the easiest way I found.  Why trust eye sight when you can get software to tell you what the true focus is.

 

Dan



#13 sternenhimmel

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Posted 16 April 2024 - 12:57 PM

Last night I did this using the star width measurement on the guide page in ASIAIR (PHD2). It was ok, but not super easy. Basically I would adjust the focus a little, let it settle, and try to eyeball an average value, then repeat. 

I still feel like I'm not quite getting focus right on my guide scope, so I just upgraded to a 50mm with a better focuser on it. We'll see how that goes. I also think I need shorter exposures for my AM5, so this will help with that too. 



#14 Oort Cloud

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Posted 16 April 2024 - 02:20 PM

Last night I did this using the star width measurement on the guide page in ASIAIR (PHD2). It was ok, but not super easy. Basically I would adjust the focus a little, let it settle, and try to eyeball an average value, then repeat.

I still feel like I'm not quite getting focus right on my guide scope, so I just upgraded to a 50mm with a better focuser on it. We'll see how that goes. I also think I need shorter exposures for my AM5, so this will help with that too.

You realize there is a focus routine in AA, right? Focus, PA, Preview, Autorun, Plan, Video, Live.

When you choose focus, it uses an ROI, so make sure you have the star inside the green box before you start. Then, not only can you see the star (zoomed in, too), but you also have FWHM and peak values to work with as well (you want the former to be low, and the latter high).

Much easier that using the guiding interface. Now with PHD2 (what the ASIair is running under the hood), you can get all that from the main screen if you ever switch from air to a miniPC.

Edited by Oort Cloud, 16 April 2024 - 02:21 PM.

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