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Finder scope placement for Sharpcap Polar Alignment

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#1 Lornet

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Posted 14 May 2021 - 10:52 AM

To get a good polar alignment with Sharpcap, does it matter where on the OTA you place your finderscope and camera?  I have an ES  AR127 and currently have my finder scope attached to the handle that is part of the mounting rings.  In other words, it's on top of the scope.  It occurred to me that the placement of the scope was not close to the polar alignment scope in the mount.  Does this make a difference that I would notice?

LT



#2 Dynan

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Posted 14 May 2021 - 11:03 AM

That shouldn't matter since you are positioning the mount, not your scopes (as long as they aren't too far apart in FOV).

 

I use my main camera (ASI183 or ASI533) with my ED ED127. Works fine. I bump the gain up to ≈500 and can loop at 4 seconds.


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#3 jrschmidt2

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Posted 14 May 2021 - 11:26 AM

Sharpcap uses the rotation of the scope ABOUT the RA axis (when you turn the mount) to gauge the alignment.  So the exact position doesn't matter.  It also (apparently) doesn't even matter whether the guide scope (or the main scope itself) is perfectly aligned along the RA axis either.  Either way, whole setup is rotated about the RA axis when you turn the axis during the PA process.


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#4 alphatripleplus

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Posted 14 May 2021 - 12:43 PM

Yes, placement doesn't matter as long as the camera/scope you are using points to within 5 degrees of the pole, and the FOV of the camera/scope combo is between 1 and 2.5 degrees. (I've been successful using a FOV as small as 0.5 degrees though).


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#5 MCinAZ

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Posted 15 May 2021 - 05:19 PM

  If you're using a camera mounted on the telescope, it's important to ensure that nothing shifts as the mount is rotated in RA during the alignment process. Any mechanical displacement due to deflection or backlash will complicate the alignment process. Consequences could range from inability to eliminate the last little bit of offset to highly confusing (and frustrating) results if the shift changes the direction the alignment camera is pointing by more than a few arc-min. If you have a well-made, solid mount, there should be no issues, but something to consider.

 

  I modified a polar scope cap for my Losmandy mounts so that I could mount my polar alignment camera directly to the RA assembly. That eliminates any possibility of errors introduced by the declination axis mechanism, as well as the need to mess with balance or mounting the camera and lens on the telescope.

 

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#6 alphatripleplus

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Posted 15 May 2021 - 05:38 PM

+1.

 

Yes, if there is any flexure in the support for the camera/guide scope (or finderscope) as the mount is rotated in RA, that will potentially lead to PA errors. 




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