Polar Alignment Without Polaris

Using SharpCap's Polar Alignment feature
RMSQueenMary
Posts: 33
Joined: Mon Jan 15, 2018 4:58 am

Re: Polar Alignment Without Polaris

Post by RMSQueenMary » Sun Dec 23, 2018 4:55 am

turfpit wrote:
Tue Aug 14, 2018 9:56 am
What mount do you have?

I used to own a Celestron CG5 and now have a Celestron AVX equatorial mount. These mounts have a facility called All Star Polar Align (ASPA). I have used this to good effect. ASPA works by allowing the user to select any star in the sky and use that in combination with the Alt/Azm adjusters to achieve polar alignment. I use ASPA with a camera inserted in the scope rather than an eyepiece. Turning on the reticule in the capture software increases the accuracy. The steps I take are:
  • Get rough polar align by looking through the mount's polarscope or the vacant polarscope slot.
  • Fit camera into scope and turn on software reticule.
  • Slew to appropriate star (I am using Altair or Deneb in August for polar alignment).
  • Follow the handset instructions via ALIGN > POLAR ALIGN.
  • Get the handset to report the PA accuracy.
The process takes < 5 minutes.

I commonly get reported alignments like this:

ASPA-result.JPG


I regularly achieve accuracy of 1", 1" and have managed 1", 0". I have never got 0",0" but given the courseness of the Alt/Azm lever threads not surrprising. I don't know/care how the accuracy stacks up against other PA methods but it works for me and had zero cost above the original equipment purchase.

So how accurate is this method? See my Astrobin https://www.astrobin.com/users/turfpit/. The M31 is 60x60s unguided - which looking at the stars seems good enough. Several other images are 30x60s, which again don't seem to have star trails. I consistently get decent results with 60x60s using ASPA.

I carry out mount alignment (2 alignment stars + 4 calibration stars) with the camera in place. This eliminates optical shifts when changing from eyepiece to camera and is a more comfortable way to align.

Why am I not using Sharpcap's PA? Because 1) I have only just purchased a guide scope, 2) I sometimes capture on a Linux laptop.

I suppose other mounts will have a similar facility. Hope this gives you some ideas.

Dave
I use ASPA with the eyepiece, I usually get it around 3. The Azimuth can be really frustrating.

I should try the method you use next time.

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turfpit
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Joined: Mon Feb 13, 2017 8:13 pm
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Re: Polar Alignment Without Polaris

Post by turfpit » Sun Dec 23, 2018 11:29 am

RMSQueenMary

I am at 53 N and kneeling on a hard, damp surface leaning back at 37 degrees is not my idea of a good time. To help with comfort I made one of these http://www.stark-labs.com/craig/lybar/lybar.html. I made the mark 2 so I have 12", 16" and 20" heights - mine is glued (Gorilla glue) and screwed so is very robust. I use the chair to eyeball Polaris through the polar scope. This is always the start of my imaging session now:

setting up 2.png
setting up 2.png (632.53 KiB) Viewed 353 times

I sight on the mast array on top of the building (which is about 1 mile away). That gets my RDF and scope aligned and focused. Swap eyepiece for imaging camera (include all optics like flatteners/reducers at this stage). Start capture software, select largest capture area & turn on reticule. Refocus scope to get the image shown in the capture. Scope is now good enough focus for stars used in the mount align process. Once aligned (I use 2 + 4 on my Celestron AVX) I then carry out ASPA. Other mounts have similar functions which will be described in the relevant manuals.

I came up with this method because aligning with the eyepiece and then swapping to the camera always resulted in an image shift which meant slewing was never dead centre and seeing as most of the objects we image aren't very visible, slewing accuracy is paramount.

It works for me https://www.astrobin.com/372374/?nc=user 9x600s (yes 10 minutes) unguided and no real overhead in alignment time.

The other benefit here is that polar alignment can be carried out without sight of the pole star.

These 2 images show the drift on a set of 180s exposures after 1 hour.

1-hour-capture.JPG
1-hour-capture.JPG (68.24 KiB) Viewed 353 times


QHY have a gizmo that fits up the polar scope housing. It is in effect a camera plus software which runs on Windows or Linux. Down sides are it relies on being able to see the pole and costs £300. To me an extra layer of complexity and everyone one here knows how I view self inflicted complexity

Good luck with it - wishing you all the best for Christmas and the New Year.

Dave

RMSQueenMary
Posts: 33
Joined: Mon Jan 15, 2018 4:58 am

Re: Polar Alignment Without Polaris

Post by RMSQueenMary » Tue Dec 25, 2018 3:32 pm

turfpit wrote:
Sun Dec 23, 2018 11:29 am
RMSQueenMary

I am at 53 N and kneeling on a hard, damp surface leaning back at 37 degrees is not my idea of a good time. To help with comfort I made one of these http://www.stark-labs.com/craig/lybar/lybar.html. I made the mark 2 so I have 12", 16" and 20" heights - mine is glued (Gorilla glue) and screwed so is very robust. I use the chair to eyeball Polaris through the polar scope. This is always the start of my imaging session now:


setting up 2.png


I sight on the mast array on top of the building (which is about 1 mile away). That gets my RDF and scope aligned and focused. Swap eyepiece for imaging camera (include all optics like flatteners/reducers at this stage). Start capture software, select largest capture area & turn on reticule. Refocus scope to get the image shown in the capture. Scope is now good enough focus for stars used in the mount align process. Once aligned (I use 2 + 4 on my Celestron AVX) I then carry out ASPA. Other mounts have similar functions which will be described in the relevant manuals.

I came up with this method because aligning with the eyepiece and then swapping to the camera always resulted in an image shift which meant slewing was never dead centre and seeing as most of the objects we image aren't very visible, slewing accuracy is paramount.

It works for me https://www.astrobin.com/372374/?nc=user 9x600s (yes 10 minutes) unguided and no real overhead in alignment time.

The other benefit here is that polar alignment can be carried out without sight of the pole star.

These 2 images show the drift on a set of 180s exposures after 1 hour.


1-hour-capture.JPG



QHY have a gizmo that fits up the polar scope housing. It is in effect a camera plus software which runs on Windows or Linux. Down sides are it relies on being able to see the pole and costs £300. To me an extra layer of complexity and everyone one here knows how I view self inflicted complexity

Good luck with it - wishing you all the best for Christmas and the New Year.

Dave
Thank you Dave. I use the Revolution Imager R2 and Starsense in lieu of 2+4 star alignment with the CGEM2 mount. That saves a lot of time. 8-)

I find the azimuth part more difficult than altitude. You got to turn the knobs east or west.

Merry Christmas and Happy New Years to you.

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