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Beginning Autoguiding

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#1 Stargazer3236

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Posted 06 December 2021 - 10:09 PM

I want to start to begin auto-guiding. My camera will be an ASI174mm mini camera attached to a 30mm F/4 guiding scope. The mount is a Skywatcher EQ6R and the scope will be a C11, using an ASI533MC Pro camera for imaging. I want to use SharpCap Pro for stacking long exposures.

 

What connections do I make between the guide camera and the mount?

 

What is good guiding software?

 

What specifics do I need to understand before undertaking this next step?

 

Thanks for your advice and suggestions.



#2 DivisionByZero

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Posted 06 December 2021 - 10:19 PM

I can't quite remember if PHD2 has the option to guide via the mount or not.  If it does, then you only need a usb connection to the guide camera and whatever it is you are using the connect to the mount as the guide commands will be sent to the mount directly.  Otherwise, guide cameras have a guide port which is a small cable (looks like an old telephone cable if you're old enough to remember those) and guide commands can be sent from the camera directly to the mount.

 

PHD2 is excellent and very common.  I use INDI/EKOS's internal guider, myself, though.

 

Probably the most important thing to keep in mind is that it will take you some time to really make the guiding work. It's like most other parts of the hobby that we are mixing and matching so much equipment that it inevitably requires some tweaking, fiddling, cursing, and sobbing to make it all work together.

 

The other thing to keep in mind is that you should make sure to have enough power and bandwidth for all your cameras.  Some computer control systems can go unstable or create strange results if there are power problems.


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#3 KungFood

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Posted 06 December 2021 - 10:23 PM

You should not have to make any connection from the guide cam to the mount with your gear. You can get a small usb 3 hub, and run your mount, imaging camera, and guide cam to the hub, then a single usb connection from the hub to your computer.

 

Guiding software is easy, PHD2

 

Sharpcap is good for a lot of things, EAA for example. But if you are wanting to do traditional AP, something else is preferable. I use NINA, it's full featured, free and well supported. There are other option though, APT, SGP, etc. This is really only the acquisition software though, stacking and processing is done with other software. Free options for stacking are DeepSkyStacker, ASTAP, and others. Image processing can be done in Photoshop, Startools, AstroPixelProcessor, and the gold standard, Pixinsight (very not free, in both currency and learning curve)



#4 Cfreerksen

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Posted 06 December 2021 - 10:56 PM

With a C11 I would skip the guide scope. You need an OAG. Mirror flop will no doubt be a problem.

 

https://www.cloudyni...nd-image-shift/

 

Chris


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#5 arbit

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Posted 06 December 2021 - 11:01 PM

Guiding options are via ST4 (camera to mount cable), or via ASCOM (camera to PC with or without hib as described above).

ASCOM is generally preferred.

Guiding software (unless you are already using something.like Maxim).
1. PHD2 - most common, lots of support, easy to use, getting the right configuration cam be surprisingly tricky.
2. INDI /EKOS suite - never used it, but as far as I know has good support.
3. Metaguide - Less common, UI needs time to get used to, I found it better performance for low end mounts.

All will need tuning for your mount. Probably best to start with PHD2, run the guiding assistant etc to understand the guiding limitations / parameters and see what happens. Any initial questions can be posted here on on the PHD2 forums.

If PHD2 doesn't work for you, can try one of the others.



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#6 DuncanM

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Posted 07 December 2021 - 12:18 AM

I want to start to begin auto-guiding. My camera will be an ASI174mm mini camera attached to a 30mm F/4 guiding scope. The mount is a Skywatcher EQ6R and the scope will be a C11, using an ASI533MC Pro camera for imaging. I want to use SharpCap Pro for stacking long exposures.

 

What connections do I make between the guide camera and the mount?

 

What is good guiding software?

 

What specifics do I need to understand before undertaking this next step?

 

Thanks for your advice and suggestions.

The ASI174mm is way overkill for a 30mm F4 guidescope. The ASI120mm mini would perform just as well, for somewhat less $$. OTOH, if you use an OAG then the 174 is a better bet.



#7 CoyoteVB

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Posted 07 December 2021 - 12:55 AM

I highly recommend OAG.  I tried guiding with a small guide scope that works great with my WO GT71 but with my EdgeHD 8 the results were not acceptable.   The resolution of the GT 71 is something like 1.61 arc sec and that allows for ok guiding.   The focal length between the guide scope and main scope was just to much.  With the resolution of your C11  guiding will need to be good.   Pairing the ASI174 with the OAG worked well for me as long as seeing conditions are good.  I am still a beginner and learning a lot.  My current challenges are improving guiding and post processing.



#8 Tapio

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Posted 07 December 2021 - 01:15 AM

That small 30mm F/4 guiding scope is not going to work when imaging with C11.
As others have said your best option is to use OAG.

And hope you have focal reducer because with asi533 you have very narrow field.

#9 the Elf

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Posted 07 December 2021 - 01:37 AM

I also recommend OAG.

Here are two videos I made some time ago. Maybe you pick up something helpful.

https://www.youtube....h?v=S3lZcLt_zDU

https://www.youtube....h?v=vob9IW9i4uc


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#10 F.Meiresonne

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Posted 07 December 2021 - 06:35 AM

Guess indeed for 8" or bigger SCT/RC OAG is the way to go...

 

I don't use those so my guiding with a guide scope works well. Still i opted at least for a guide scope with FL of 280mm and a more sensitive ASI 290 mini over the 120 asi mini.

Sofar no issues, even in my 130 mm/F7 it seem to work well on M92...

 

I am in the market for a second guide system for my smaller scopes, still don't know what i will take...the zwo 60 mm f=280 is no longer available unfortunately...



#11 TelescopeGreg

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Posted 07 December 2021 - 01:23 PM

The ASI174mm is way overkill for a 30mm F4 guidescope. The ASI120mm mini would perform just as well, for somewhat less $$. OTOH, if you use an OAG then the 174 is a better bet.

The issue here isn't the camera, it's the guide scope's focal length.  In summary, two issues have been noted.

 

One is that the guide software (PHD2) needs to be able to know where the stars are to a sufficient precision to guide the imaging system.  That boils down to wanting the scale of what each pixel in the guider sees of the sky to be no more than about 5x larger than that of the imager.  Pixel scale is 206 * pixel size / focal length.  Calculate that for both the guider and imager and look at the ratio; it needs to be about 5:1 or less.  The OP's suggested configuration is far too high to be accurate enough for effective guiding.  Moving to an OAG configuration uses the imaging optical path for the guider too, so that ratio reduces to simply the ratio of the pixel sizes, which will be well within the 5:1 guideline.

 

The second issue is that some OTAs (SCTs, typically) have a mirror which can move slightly as the night progresses.  That can affect where the image hits the main imaging camera (which will affect the final image), but the guide scope and camera will have no clue what's going on because it has an independent view.  Using an OAG, where the optical path for guiding is the same as that for the imaging, allows the guider to see the movement and issue corrections for it.



#12 DuncanM

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Posted 07 December 2021 - 03:31 PM

The issue here isn't the camera, it's the guide scope's focal length.  In summary, two issues have been noted.

 

One is that the guide software (PHD2) needs to be able to know where the stars are to a sufficient precision to guide the imaging system.  That boils down to wanting the scale of what each pixel in the guider sees of the sky to be no more than about 5x larger than that of the imager.  Pixel scale is 206 * pixel size / focal length.  Calculate that for both the guider and imager and look at the ratio; it needs to be about 5:1 or less.  The OP's suggested configuration is far too high to be accurate enough for effective guiding.  Moving to an OAG configuration uses the imaging optical path for the guider too, so that ratio reduces to simply the ratio of the pixel sizes, which will be well within the 5:1 guideline.

 

The second issue is that some OTAs (SCTs, typically) have a mirror which can move slightly as the night progresses.  That can affect where the image hits the main imaging camera (which will affect the final image), but the guide scope and camera will have no clue what's going on because it has an independent view.  Using an OAG, where the optical path for guiding is the same as that for the imaging, allows the guider to see the movement and issue corrections for it.

Software can determine centroid precision to much better than typical seeing, even with a 120mm guidescope and a camera with 3.75 micron pixels. This is why astronomical seeing conditions can be monitored with great accuracy with very short EFL cameras and the equivalent of a ASI 120mm mini camera.* The idea that you need 1/5 or even 1/10th the imaging system focal length is a myth:

 

http://lhastro.org/c...Guide-Scope.pdf

 

The problems arising from SCT mirror movement and potential flexure are not myths (but can be minimized with shorter but more numerous sub exposures in the imaging camera) which is why OAGs are still preferred. However the issues with OAGs revolve around sensor area vs sensitivity so that guidestars can be found in the limited FOV of an OAG, when working with long EFL imaging systems. 

 

* https://www.sbscient...eing-monitor-2/


Edited by DuncanM, 07 December 2021 - 03:45 PM.


#13 the Elf

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Posted 07 December 2021 - 04:16 PM

There are two ways to off axis guide. a) plan before, know where a bright star is and find it in the guide camera. b) throw money at the problem and get a very sensible guide camera. In that case you will find guide stars almost everywhere. I'm on a).



#14 DuncanM

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Posted 07 December 2021 - 05:12 PM

There are two ways to off axis guide. a) plan before, know where a bright star is and find it in the guide camera. b) throw money at the problem and get a very sensible guide camera. In that case you will find guide stars almost everywhere. I'm on a).

 

I find that even at ~1700mm EFL that I can find a guide star in almost any random OAG FOV using an ASI 120mm mini and a 10in SCT at ~F7 using camera 2x2 binning. Astroart 8 has recently implemented additional 2x2 software binning and that has improved sensitivity somewhat, as well. However a guidecamera with a larger sensor and equal or better QE is on my wish list. I use an older CCD imaging camera with high read noise so I have to use long subs to minimize the read noise and for that I need to use an OAG. 




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