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Autoguiding with a partially obstructed view

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#1 justinvoelker

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Posted 01 August 2020 - 02:03 PM

After having slowly advanced my astrophotography hobby over the past few years, I am now trying to really tighten up some weak areas. One of those, is guiding. Specifically, guiding in my exact backyard.

 

The attached photo is standing next to my pier facing directly north. Polaris is right between the 3rd and 4th power line (from the bottom). I'm not worried about these lines in images since stacking completely eliminates them. However, guiding can be a pain. Once the guide star hides behind a power line, PHD2 throws a hissy fit. Once the star comes back out (maybe 30-60 seconds later), I simply select the star again and continue imaging. Typically, only one light frame is lost, maybe two depending on when guiding went haywire. I've even preemptively selected a different star before my ideal star went into hiding but don't want to manually do that over the course of an imaging session.

 

I would like to start leaving my imaging sessions running for longer periods of time without any baby sitting. Is there anything I can do inside PHD2 to tell it "you're going to lose the star and that's okay--it'll be back soon so just wait a minute and pick up where you left off when it returns?"

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#2 Tapio

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Posted 01 August 2020 - 02:34 PM

You need something like SGP, ie automation software which can recover from situation like this.

#3 justinvoelker

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Posted 01 August 2020 - 04:04 PM

Actually, I am using SGP. Perhaps it handles this situation if I just leave it alone long enough? I guess it seems like once PHD2 loses the star, it just stays unguided until I reselect a star.

#4 Alex McConahay

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Posted 01 August 2020 - 04:10 PM

Tell PHD2 to ignore the brightness of the star....I forgot which checkbox it is.  (and it is actually disabling something that is normally enabled--but without my computer to look it up, I forget. ) 

 

At any rate, I don't think a power line would completely blank out a star for very long, maybe one exposure. And SGP should be able to ride through that. If not, Recovery will get you through although take up time you don't need to waste. 

 

And besides, maybe you need to consider not imaging when the target gets that low. (although that is easy for me to say. I don't know what other obstructions you have up there.) 

Alex



#5 justinvoelker

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Posted 01 August 2020 - 05:56 PM

Thanks Alex. Unfortunately, that's a 150' pole and essentially directly in my field of view. Imaging through the lines is not low in the horizon by any means. I live at 43°N and this photo is taken at basically a 45° angle to the ground. Also, they thick, high voltage lines and do a pretty good job of completely blocking the star long enough for guiding to freak out.

 

I'm guessing the setting you mentioned disabling is "star mass detection," correct? I'll have to give that a shot and see what luck we have. That plus just letting SGP figure life out may be enough.



#6 StephenW

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Posted 01 August 2020 - 07:18 PM

>I am using SGP. Perhaps it handles this situation if I just leave it alone long enough?

 

Yep, SGP already handles it.   I also have to guide through some wires for certain parts of the sky - guiding is lost for multiple seconds, but PHD2 and SGP recover once the guide star becomes visible again.



#7 Alex McConahay

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Posted 01 August 2020 - 07:19 PM

Yes, I think “Star massdetection “ is what you want. I go a long time without needing to look at these parameters. It will help if the lines are just dimming the star. Not if they are obscured completely. Certainly SGP can overcome this, but a recovery can take several minutes, plus the time you specify for waiting between recovery attempts. Looking at the multiple cables, it looks like you would have a series of such incidents.

Alex

#8 justinvoelker

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Posted 01 August 2020 - 09:22 PM

Yep, SGP already handles it.   I also have to guide through some wires for certain parts of the sky - guiding is lost for multiple seconds, but PHD2 and SGP recover once the guide star becomes visible again.

Is there anything you had to configure to get SGP and PHD2 to recover? I think maybe I've just never given them enough time to recover on their own and always jump in with a manual fix.

 

It will help if the lines are just dimming the star. Not if they are obscured completely.

Unfortunately they completely obscure even bright stars so I guess that won't help. Thanks for the thought though.



#9 Alex McConahay

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Posted 01 August 2020 - 10:15 PM

>>>>Is there anything you had to configure to get SGP and PHD2 to recover?

 

Yes, you have to tell SGP to use the Recovery mode. See the part illustrated in the Highlighted red  "E" in the image below. The caption for that option is as follows:

 

To have SGP continue to take calibration frames even if the weather
otherwise shuts down the run, add the calibration frame specs to the sequence (A),
and under “Main Menu/Tools/Options” (B and C), check “Capture Calibration
Frames Even If Sequence Fails to Complete” (D). Note also where SGP can be told
to “Attempt to Automatically Recover the Sequence” (E) should weather or some
other problem cause a premature stop.

 

Alex

 

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#10 AstroBruce

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Posted 02 August 2020 - 06:28 PM

I don't understand how you can completely lose the guide star. Unless your guidescope aperture is less than the diameter of the power line, The power line can only reduce brightness by its own width compared to the aperture of the guidescope. 

 

Bruce




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