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Keeping Planet Centered during a Imaging Run

Cassegrain Celestron Imaging Planet SCT
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#1 sandconp

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Posted 16 June 2021 - 12:09 PM

I have been using both Sharpcap and Firecapture  to do planet imaging.  Firecap seems to work better for me since it has an option to keep the planet centered during the imaging of my capture which is usually 1 to 2 minutes.  Using either product, I am finding myself having to nudge the planet with the hand control before it goes off the screen.  I am using a Celestron CPC1100.  The problem seems to be worse when I am using a 2X barlow because the image is magnified. 

 

Could this be related to my backlash setting(s)?  How can I keep the image from scrolling off my screen in either Sharcap or Firecapture?


Edited by sandconp, 16 June 2021 - 12:10 PM.


#2 Tapio

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Posted 16 June 2021 - 12:40 PM

Do you have a wedge? If so then how is your PA?
I believe you can do autoguiding too with SC/FC but haven't tried it (no need with my fl).

#3 KTAZ

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Posted 16 June 2021 - 12:50 PM

This is a common problem for FireCapture users. There are a few settings in FC that can help. 

 

Under "Autoguiding" settings, you can select "Swap direction" on either the RA or DEC axis if the movement is opposite of what it should be. That often causes the drift when FC sends a command to move the scope back towards the target, but the pulse is in the opposite direction, driving it away.

 

Also, try checking the "Prefer 'MoveAxis' to 'PulseGuide'" and see if that corrects the problem.



#4 sandconp

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Posted 16 June 2021 - 12:59 PM

Do you have a wedge? If so then how is your PA?
I believe you can do autoguiding too with SC/FC but haven't tried it (no need with my fl).

I am using a CPC1100 which is an Alt-Az Mount so there is no polar alignment.



#5 KiwiRay

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Posted 16 June 2021 - 01:11 PM

I frequently have to nudge the planet to keep it within the ROI window, and it's just part of the process for me. I know FC has a way to get the window to track the planet, but I've not been able to get that to work.



#6 cmooney91

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Posted 16 June 2021 - 01:16 PM

SharpCap has an experimental feature called "feature tracking"  

 

If you can connect and control your mount from your PC, then SharpCap can keep a planet or crater centered automatically, using the high speed frames from the main imaging camera. 


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#7 Gary Z

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Posted 16 June 2021 - 01:30 PM

 

Could this be related to my backlash setting(s)?  How can I keep the image from scrolling off my screen in either Sharcap or Firecapture?

Backlasth.  Do you have any backlash?

 

There is a feature in the hand control settings called calibrate goto.  This is a very useful feature when changing configurations depending on what you want to image with or do visual with.  it helps with the load.  The manual does cover this on other mounts like the SE/ and maybe the Evolution, but I don't know about the CPC.  I do it before doing any alignment.  It does not take long.  

 

Gary



#8 RedLionNJ

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Posted 16 June 2021 - 01:39 PM

I very much doubt this symptom is due to backlash. If you had delays of seconds due to backlash, no imaging would be possible.

 

If you're trying to keep the planet centered using MoveAxis, be aware not every mount driver supports this, particularly in AltAz mode. In such a situation, you may get a more usable result via PulseGuide on the autoguider port.

 

I'm one of those "unfortunates" where my GEM doesn't supply an option FireCapture can use.  But fortunately, the tracking is quite good enough to keep a planet near the center of the field for several minutes or even hours at a time, at least over most of the sky.



#9 Ittaku

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Posted 16 June 2021 - 03:27 PM

Unfortunately it's simply the nature of alt az mount movement accuracy at the high magnifications we capture planets at. The best you can do is be as critical as possible with your alignment before starting. I moved to a wedge which improved tracking dramatically, but for the sake of 1-2 minute captures, you're best just monitoring it and nudge it with the hand controller to keep the planet in the centre. At the high frame rates we capture (mostly), the movement has no effect on the quality of the capture. Unfortunately you cannot use the autoalign feature in FC as Celestron alt az mounts do not accept autoguiding unless they have a wedge installed.

 

Note that since you have a 183MC (which I also have) if you're not so aggressive with your frame rates, and aim for say 30fps (set exposure to 33.3ms) and set the ROI to a smaller but still massive 4k (3840x2160), then you can use the cut-out feature (the scissors) and it will track the planet across the huge field for much longer before it runs out of the field of view.


Edited by Ittaku, 16 June 2021 - 03:32 PM.

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#10 Tulloch

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Posted 16 June 2021 - 04:33 PM

I agree with most of what's above (except for the backlash comment). Regarding backlash, I have it set on 0 for both directions on my alt/az Evo mount, because I found that when it was higher it tended to jerk the scope too much which is bad at high magnifications. And anyway, the slight amount of nudging you need to do is usually the same way each time as the capture progresses (eg always up and right, or down and left) - once I have it going the right way, I select a speed of "1" (sidereal) and nudge the scope every 10 seconds or so. This keeps the planet on the sensor, but also keeps it away from the dust bunnies on the AR window/barlow/IR filter etc.

 

I have a small ASI224MC camera, and use a reduced ROI on the screen to just (say) 500 pixels high by 800 pixels wide. This increases my maximum throughput via USB3. Then I use the cutout tool in Firecapture to only record the planet and a little black space around it (say 350x350 for Jupiter, smaller for the other planets). This keeps my file sizes down and my fps rate up (150 fps for Jupiter, 100 fps for Saturn, 250 fps for Mars).

 

Don't be afraid of nudging - I recommend doing it in small movements often rather than large movements rarely.


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