Eq3 pro - polar alignment without polaris

[SStanford]

Hi all, 

I was fortunate enough to acquire an EQ3 pro with SynScan second hand from FLO last week week which arrived Friday. 

I've also bought a 12v power adapter that let's me plug it into the mains which means I've had my first play around this evening. 

I'm struggling a bit with polar alignment as I don't have a view of Polaris from my balcony. 

I'm able to level the mount well but I can't get a decent app on android that gives an estimate of Polaris without being able to see the star directly in the polar scope. I've got Star Walk 2 which tells me polaris is 51° in altitude, am I right in thinking this is what I set altitude to on the mount (with North being as accurate as possible). 

I know I'm out by quite a bit as I set "view object" to Mars before it slipped behind the clouds and, although in the right direction, was off by many degrees. 

I've been told that drift alignment works well without being in view of Polaris but can't see any guides online without proper PA initially so I'm a little stuck! 

I've also been told that, once properly PA'd I can mark the position of the tripod and leave the mount altitude settings as they are for future use. It's this the case with drift alignment too? 

I should mention that I'm interested in astrophotography so I'm aware that PA needs to be spot on. Although my current alignment is good enough even for observing! 

S. 

[JamesF]

If you're interested in astrophotography then I assume you have a computer of some sort nearby?  Given that, PHD has a drift alignment facility as far as I recall.  No need to be able to see Polaris at all.

James

[SStanford]

33 minutes ago, JamesF said:

If you're interested in astrophotography then I assume you have a computer of some sort nearby?  Given that, PHD has a drift alignment facility as far as I recall.  No need to be able to see Polaris at all.

James

That's very useful. 

Do I need to get a guide scope and guide cam for this or can I just use my DSLR plugged into the computer with PHD2 and scope for initial alignment? 

Will I need to do drift alignment everytime I setup or once aligned can I mark the tripod on the ground with the altitude left the same on the mount? 

Thanks again

[JamesF]

36 minutes ago, SStanford said:

That's very useful. 

Do I need to get a guide scope and guide cam for this or can I just use my DSLR plugged into the computer with PHD2 and scope for initial alignment? 

Will I need to do drift alignment everytime I setup or once aligned can I mark the tripod on the ground with the altitude left the same on the mount? 

Thanks again

Drift alignment is done with the main camera, not the guidescope.  Ideally you'd do it every time you set up.  You're getting down to very small fractions of one degree in terms of accuracy, so it doesn't take much movement elsewhere in the system to mess things up.

James

[SStanford]

19 minutes ago, JamesF said:

Drift alignment is done with the main camera, not the guidescope.  Ideally you'd do it every time you set up.  You're getting down to very small fractions of one degree in terms of accuracy, so it doesn't take much movement elsewhere in the system to mess things up.

James

Thanks James, much appreciated. 

So I can drift align using PHD2 with any star visible? 

I don't suppose you know of any good guides for this process? Sorry to be a pest! 

[JamesF]

You need a pair of stars.  I think the ideal is if you can pick one as close as possible to the celestial equator and as close as possible to due east or due west, whilst the other should be as close as possible to the celestial equator and due south.  It doesn't matter if you can't do that though.  It may just take more iterations to achieve a given level of accuracy.

There must be some videos on youtube demonstrating the process, quite possibly using PHD.  Hopefully I'm not confusing my software, but my recollection is that PHD does it by showing a line over a live image from the camera and getting you to move a star from one end of the line to the other using the alt and az adjusters, repeating the process east/west and south in turn until you have a level of accuracy you're happy with.  I'm not certain though, as having an observatory and mounts on fixed piers I don't have to do it very often.

James

[SStanford]

Okay, I'll do my research see if I can find a video that shows how it's done. 

Alignment is a tricky business without Polaris! Maybe I should knock a hole through my ceiling instead. 

[wimvb]

The Synscan hand controller has a built in all star polar alignment function. It's in the setup section, together with 1-star, 2-star, and 3-star alignment. Just in case you don't have a computer connected to your mount.

You do a 2-star GoTo alignment, and the HC calculates the polar misalignment. After that you use the polar alignment function. If you use a high magnification eyepiece, you can get good enough accuracy.

[SStanford]

3 minutes ago, wimvb said:

The Synscan hand controller has a built in all star polar alignment function. It's in the setup section, together with 1-star, 2-star, and 3-star alignment. Just in case you don't have a computer connected to your mount.

You do a 2-star GoTo alignment, and the HC calculates the polar misalignment. After that you use the polar alignment function. If you use a high magnification eyepiece, you can get good enough accuracy.

My thinking initially was to use this function when purchasing SynScan/go-to however I'm so far from the objects on the hand control that this function isn't very useful :(. 

[wimvb]

7 minutes ago, SStanford said:

My thinking initially was to use this function when purchasing SynScan/go-to however I'm so far from the objects on the hand control that this function isn't very useful :(. 

Even after a 2-star GoTo alignment. The way I used it was as follows.

Align the tripod and mount so that the RA axis roughly points towards the NCP.

Do a 2-star alignment with a 25 mm eyepiece. The first star will be miles out.

Redo the 2-star alignment with a (Barlowed) 17 mm eyepiece to get better alignment. The first star may still be out, but the second should be close. After this alignment, objects should be in the fov of a 25 mm eyepiece.

Do the polar alignment on any star suggested by the HC.

Redo the 2-star alignment after polar alignment.

I always considered finding the correct alignment star to be the tricky part. Make sure your finder scope is aligned with the main scope.

[SStanford]

Thanks Wimvb, 

Do you find this process to be accurate enough for AP or observing only? 

For 2-star alignment do you use any star you can see or one's that are close to celestial equator? 

[wimvb]

6 minutes ago, SStanford said:

Thanks Wimvb, 

Do you find this process to be accurate enough for AP or observing only? 

For 2-star alignment do you use any star you can see or one's that are close to celestial equator? 

For observing, definitely. You don't need accurate pa for that. I don't know if they do, but a GoTo mount is able to compensate for the drift in declination due to poor pa.

As for photography, guiding will compensate for polar misalignment as well as mount tracking errors.

 

[SStanford]

13 minutes ago, wimvb said:

For observing, definitely. You don't need accurate pa for that. I don't know if they do, but a GoTo mount is able to compensate for the drift in declination due to poor pa.

As for photography, guiding will compensate for polar misalignment as well as mount tracking errors.

 

That's very useful! Great pictures of M38. 

I was thinking of using a guide scope/camera to compensate for PA error. I was recommended the following:

https://www.firstlightoptics.com/zwo/zwo-mini-finder-guider-asi120mm-bundle.html

I'm told to look out field rotation error, have you encountered any problems with this? 

[AstroMuni]

16 hours ago, SStanford said:

but I can't get a decent app on android that gives an estimate of Polaris

I have used Skeye which also can be used as a PUSH-TO device when strapped to the scope. Skysafari is also a good software but doesnt have push-to capabilities. Synscan Pro app is also available which shows you position of Polaris in polar scope reticle.

If your budget allows it, you might wish to purchase Celestron Starsense.

Edited December 7, 2020 by AstroMuni

[SStanford]

2 hours ago, AstroMuni said:

I have used Skeye which also can be used as a PUSH-TO device when strapped to the scope. Skysafari is also a good software but doesnt have push-to capabilities. Synscan Pro app is also available which shows you position of Polaris in polar scope reticle.

If your budget allows it, you might wish to purchase Celestron Starsense.

I've just downloaded Skeye and was what I was looking for with reticle. Hopefully this will get me closer to Polaris than before, thanks a million.

I think what I'll be doing next (when skies permit):

1 - Strap my phone with Skeye to the polar scope and align as close as I can here.

2 - Run a two star alignment with a 20mm eyepiece, then another two-star alignment with a 10mm, then PA via the SynScan handcontrol on any star, then another two-Star alignment (as outlined by @wimvb above).

3 - Use tracking alignment as outlined in the video shown here (https://www.youtube.com/watch?v=YVnOF2Q6e6U) using PHD2 on any star that shows up in my DSLR attached to the software.

I'll also be adding a guidescope to my setup (second on my list of purchases!)

[AstroMuni]

If you are using PHD2 consider doing platesolving using that too. SHould help with alignment

[SStanford]

3 hours ago, AstroMuni said:

If you are using PHD2 consider doing platesolving using that too. SHould help with alignment

Platesolving; another new term!

[JamesF]

Combined with platesolving, drift alignment works very neatly.  You can use a planetarium app to find a reasonably bright star close to the ideal position, get the mount to go to it and plate solve repeatedly until it is definitely pointing at the right one, then drift align against it.

James

[wimvb]

8 hours ago, SStanford said:

I'm told to look out field rotation error, have you encountered any problems with this? 

Field rotation occurs any time you don't have perfect polar alignment. In the extreme case where you image with an altaz mount (which is always "polar aligned" to zenith), you have a large amount of field rotation. If your pa error is small, field rotation will be negligible. I think that even with a synscan all star polar alignment, which probably is less accurate than drift alignment, field rotation will not be a problem.

[AstroMuni]

5 hours ago, SStanford said:

Platesolving; another new term!

You capture an image and send to plate solving software which then matches the star pattern with star catalogue to figure out what you are looking at.

[wimvb]

53 minutes ago, AstroMuni said:

You capture an image and send to plate solving software which then matches the star pattern with star catalogue to figure out what you are looking at.

That sums it up quite nicely in a one-liner.

Edited December 7, 2020 by wimvb