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Settings and focusing for guide camera

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#1 awilliams

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Posted 11 April 2021 - 07:41 AM

Hi I'm looking for help with my guiding set up.

I have an ASI 120MM guide camera and a 60mm guide scope with helical focuser. I have managed to get it roughly focused but when I run the guiding assistant in phd2 it complains that I should improve my focus and I can could only see one star in the display. In sharpcap it seems to go between not showing up stars or having very blotchy huge stars when I increase the gain.

My question is what settings should I have on the camera in terms of gain and exposure length? Is there anything else I need to set in sharpcap and phd2? What is the best way to focus better? Can I use the focus assistant in sharpcap if I am focusing manually? Is it worth buying a bahtinov mask for this?

#2 David Boulanger

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Posted 11 April 2021 - 08:49 AM

did you try to focus on something, a distant tree, cell tower, during the day.  As far as gain goes I can't help because I currently use a different guide camera.  PHD2 always bitches at me when using the guiding assistant about my focus.  I think its more to do with the atmosphere I have here than actual focus. 



#3 NMCN

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Posted 11 April 2021 - 09:04 AM

It sounds like you're not in focus at all.  You said that in Sharpcap you go from not seeing any to huge blotchy stars when you increase the gain.  Do what David suggested -- during daylight hours, focus using a distant object.  Then you can use Sharpcap to refine if you want, but PHD2 is pretty tolerant as long as you're close.



#4 TelescopeGreg

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Posted 11 April 2021 - 01:28 PM

My best success focusing my guider was to aim at a patch of sky with a bunch of stars, and adjust the focus to maximize the number of little stars that it saw.  The tiny stars disappear when out of focus, and pretty sharply appear when in focus.  This worked better than trying to fiddle with a Bahtinov mask.

 

I did this once over a year ago, and it's still working.


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#5 Stelios

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Posted 11 April 2021 - 01:33 PM

If you have blotchy huge stars at high gain, you are grossly out of focus. Just adjust focus till stars are pinpoints in Sharpcap. 

 

If you focus during the daytime, the nighttime focus will be a bit *inward*. 

 

Remember--get those stars as small as possible! Yes, PhD2 is tolerant, but *you* shouldn't be. Give the software as much help as you can.


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#6 awilliams

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Posted 14 April 2021 - 09:15 AM

Thanks for the replies. I had another go at this and I was definitely able to move from one side of critical focus to the other while looping in sharpcap and I got the stars as small as I could. I saved a frame in phd2 this was the result. https://www.dropbox..../test image.fit

 

I ran this through SIRIL to calculate the FWHM and it comes out between 4 and 6 from 12 detected stars.

 

I'm not really sure if I'm missing something here I was adjusting the focuser back and forth as carefully as I could but this was as good as I could get it. Is this good enough? phd2 was happy guiding and sharpcap was able to platesolve for polar alignment.

 



#7 NMCN

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Posted 14 April 2021 - 06:15 PM

Thanks for the replies. I had another go at this and I was definitely able to move from one side of critical focus to the other while looping in sharpcap and I got the stars as small as I could. I saved a frame in phd2 this was the result. https://www.dropbox..../test image.fit

 

I ran this through SIRIL to calculate the FWHM and it comes out between 4 and 6 from 12 detected stars.

 

I'm not really sure if I'm missing something here I was adjusting the focuser back and forth as carefully as I could but this was as good as I could get it. Is this good enough? phd2 was happy guiding and sharpcap was able to platesolve for polar alignment.

You answered your own question.  As long as PHD2 is happily guiding and Sharpcap can plate solve, you're good to go!



#8 Stelios

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Posted 14 April 2021 - 07:11 PM

Thanks for the replies. I had another go at this and I was definitely able to move from one side of critical focus to the other while looping in sharpcap and I got the stars as small as I could. I saved a frame in phd2 this was the result. https://www.dropbox..../test image.fit

 

I ran this through SIRIL to calculate the FWHM and it comes out between 4 and 6 from 12 detected stars.

 

I'm not really sure if I'm missing something here I was adjusting the focuser back and forth as carefully as I could but this was as good as I could get it. Is this good enough? phd2 was happy guiding and sharpcap was able to platesolve for polar alignment.

PhD2 is not very sensitive to perfect focus, as it calculates a "centroid" by weighing the illumination of the pixels that the guide star covers. So you should be more than fine. 



#9 michael8554

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Posted 15 April 2021 - 10:54 AM

Simply look at the HFD reading in the PHD2 Star Profile window as you alter focus, aim for lowest HFD.

 

Hate to contradict Stelios, but the PHD2 developers are constantly telling posters to get best guidecam focus.

 

Having said that, my best HFD with an OAG is around 5, when a separate guidescope was 3. and PHD2 seems to cope...... :->




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