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Guide scope for C14

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#1 musicmatters

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Posted 25 July 2021 - 09:59 PM

I just purchased a C14 with a CGX-L mount, and will be using it for EAA and looking for the best guide scope options.  I have the Celestron .63 focal reducer and will be starting with that and a 294MC imaging camera, and a 290MM for the guide camera.  Once I can find a Hyperstar for it I will be getting that also. 
 

Which guide scopes should I be looking for to use with this setup?  If I didn’t mind spednding more money what are the higher end options?



#2 GIFTED1570

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Posted 25 July 2021 - 10:29 PM

unfortunately for such focal length anything under 80mm guidescope will be useless unless major tweaking on PHD, the best option for those is an OAG


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#3 bobzeq25

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Posted 25 July 2021 - 11:57 PM

unfortunately for such focal length anything under 80mm guidescope will be useless unless major tweaking on PHD, the best option for those is an OAG

For traditional imaging, sure.  But EAA may be a different story.  The EAA forum could advise.



#4 carolinaskies

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Posted 26 July 2021 - 02:21 PM

The old standby guiding was always the ST80 with 120mm for SCTs.  And you can throw a barlow in front of the camera as needed for particular FL parity.  

These days if you want to do double duty then I'd make it a WO 71mm or something and you could use it double duty.    

Like any imaging, even for guiding, matching the pixel resolution with the guide scope yields the best results.  



#5 Peterson Engineering

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Posted 26 July 2021 - 02:48 PM

Once upon a time, when photos were manually guided, the rule of thumb was that the guide scope should be approximately 1/2 the focal length of the imaging scope.  With the way guide software integrates star centers That's no longer necessary.  But think about it.  The higher the magnification the better the resolution and the finer the guiding.

 

My 14" Meade mounts a $119 Orion 80mm f/11.3 guidescope (91mm focal length)  And paired with an ASI 174MM guiding is pretty darned good.  This scope is no longer sold by Orion but there are a couple of identical scopes available.  The scope only weighs 3#.  And part of the beauty of this scope is that it's long enough that it mounts with 2 inexpensive ScopeStuff rings fastened to the castings at either end of the 14".  No heavy dovetail needed.

 

Yes, very small very short scopes are being used for guiding.  But I believe that a longer focal length still provides greater sensitivity when it comes to guiding..



#6 blazek

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Posted 04 August 2021 - 11:47 PM

Would you consider going OAG route instead of guiding scope? Celestron OAG (or any other with large prism ) should do the trick. You have to get good guiding camera either way . ASI 174mini is one of possible candidates.



#7 musicmatters

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Posted 04 August 2021 - 11:48 PM

What if I wanted to use it with Hyperstar?  



#8 blazek

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Posted 05 August 2021 - 12:12 AM

In the case of Hyperstar one can't use OAG, indeed . I do not have experience with Hyperstar , but in reality, you are going to "burn" everything with long exposures and perhaps exposures will be up to the minute. I wonder if one need guiding at all with Hyperstar


Edited by blazek, 05 August 2021 - 12:13 AM.


#9 alphatripleplus

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Posted 05 August 2021 - 07:29 AM

Do you intend to do EAA or traditional imaging with your C14?



#10 musicmatters

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Posted 05 August 2021 - 07:32 AM

Almost exclusively EAA

 

I understand that I may not need it w/Hyperstar.  What about when I use the .63 Reducer?  Would the Primaluce 60 work?



#11 alphatripleplus

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Posted 05 August 2021 - 09:54 AM

It's going to depend on how long your sub-exposures are, the pixel scale of your camera at the effective focal length you are using, and how smooth the tracking of your mount is. Have you measured the smoothness of your mount's periodic error curve?

 

For example, the C14 @ f/6.3 has a focal length of 2,240mm and with the 3.9 micron pixels of your Nikon 7200, you will have a pixel scale of about 0.36 arcsecs/ pixel. So if you are using 10sec to 20sec sub-exposures, a mount with a jagged PE curve might have several arcsecs of motion over 10-20 sec that would be noticeable as elongation in RA at that pixel scale. Whereas a mount with a very smooth PE curve (no spikes), might let you get away without guiding for short subs. 

 




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