Polar Alignment Without Polaris

Using SharpCap's Polar Alignment feature
noobzai202
Posts: 5
Joined: Mon Aug 13, 2018 3:03 pm

Polar Alignment Without Polaris

Post by noobzai202 » Mon Aug 13, 2018 3:07 pm

Hi everyone, I have a question here. Is it possible for SharpCap to perform Polar Alignment without Polaris? Im currently living in Malaysia and Polaris is hardly visible. Please help :) Thanks!

User avatar
turfpit
Posts: 645
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: Polar Alignment Without Polaris

Post by turfpit » 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
ASPA-result.JPG (33.01 KiB) Viewed 1093 times

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

noobzai202
Posts: 5
Joined: Mon Aug 13, 2018 3:03 pm

Re: Polar Alignment Without Polaris

Post by noobzai202 » Tue Aug 14, 2018 12:24 pm

Hi im currently using EQ3 Mount. My controller is Synscan

User avatar
turfpit
Posts: 645
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: Polar Alignment Without Polaris

Post by turfpit » Tue Aug 14, 2018 1:21 pm

Have a look at this https://www.myastroshop.com.au/guides/s ... gnment.pdf.

Google synscan all star polar align for more info (looks the same steps as the Celestron) . This function might be dependent on firmware version of the hand controller.

Dave

noobzai202
Posts: 5
Joined: Mon Aug 13, 2018 3:03 pm

Re: Polar Alignment Without Polaris

Post by noobzai202 » Tue Aug 14, 2018 1:56 pm

the problem is that i always have problem with 3 star alignment or 2 star.... it will always be poor and when it slews, its totally out.

User avatar
turfpit
Posts: 645
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: Polar Alignment Without Polaris

Post by turfpit » Tue Aug 14, 2018 4:26 pm

This is what I would try next but YMMV:
  • Make sure the mount is level, use a spirit level other than one in the mount.
  • Use a compass to get the mount pointing north.
  • Set the latitude using the scale on the mount.
  • Carry out the alignment using 2 or 3 stars.
  • Perform the ASPA. This now means a decent polar alignment.
  • Redo the alignment using 2 or 3 stars (I always do a minimum of 2 west of the meridian and 2 east of the meridian .
Dave

User avatar
admin
Site Admin
Posts: 2505
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Polar Alignment Without Polaris

Post by admin » Tue Aug 14, 2018 4:40 pm

To just answer the original question - sadly the answer is no, if you haven't got a usable view of the polar region of the sky then the SharpCap polar alignment routine cannot work, sorry.

Robin

noobzai202
Posts: 5
Joined: Mon Aug 13, 2018 3:03 pm

Re: Polar Alignment Without Polaris

Post by noobzai202 » Tue Aug 14, 2018 10:24 pm

I'm only able to see north very close to seeing polaris

noobzai202
Posts: 5
Joined: Mon Aug 13, 2018 3:03 pm

Re: Polar Alignment Without Polaris

Post by noobzai202 » Tue Aug 14, 2018 10:24 pm

The latitude scale on my mount is not accurate at all...

User avatar
admin
Site Admin
Posts: 2505
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Polar Alignment Without Polaris

Post by admin » Wed Aug 15, 2018 6:12 am

Hi,

the best thing to do is to try - you don't need to have a SharpCap Pro license to *measure* how good your current polar alignment is using SharpCap (the Pro License is only needed for the final adjustment stage). If the measurement works without any problems then the final adjustment stage should work too. You will need to be able to get an area within 5 degrees of the pole in view and see enough stars on screen for the plate solving to work (that might be a challenge low down near the horizon). Also make sure you set your lat/longitude in the settings and enable correction for refraction.

cheers,

Robin

Post Reply

Who is online

Users browsing this forum: No registered users and 0 guests