Polar alignment accuracy

[jambouk]

Has anyone done any reliable comparisons of the different methods of polar alignment (polar scope with the eye, polemaster, sharpcap method, drift aligning) and shown the reproducibility of each and the accuracy of the alignment?

I'd be interested to see such data.

James

 

[Ronclarke]

So would I! 

I've been using the polar scope by eye and getting 10 min subs without a problem or buying expensive add-ons.. 

 

Ron

[PaulR1]

I do by eye and easy do 5 min subs , never tried 10 but It would probably be ok .

I am using sharpcap now , well I will when these damn clouds go and really not sure if it will make a difference but at a tenner a year I feel its a way to support the developer.

A lot of this "aiming for perfect numbers" I think is sometimes really not necessary, folks get hooked into a kind of ocd over it which ends up costing unnecessary £££'s

[Skipper Billy]

No scientific data but my personal experience is that Polemaster will get you very close very quickly. Sharpcap will get you possibly even closer just as quickly. Drift aligning gives the best result but is time consuming.

If I was mobile imaging I would use Polemaster or Sharpcap.

I am lucky to have an observatory and I drift align  at the start of each season and recheck with Sharpcap after each earth tremor (quite often around here!)

[gonzostar]

With my eyesight Polemaster has being great, takes under 10mins to do and can get good data with 5min subs. Could go longer but for light pollution!

[jambouk]

Ron, do you do a three star alignment with the mount after your eye ball polar alignment, if so what vales for Mel and Maz does the handset typically give you? Using the Polemaster I usually (and reliably) see values of under 3 arcminutes and often nearer 1 arcminute or less if the routine is done very carefully. I just wonder what are the typical values for eye ball method, and following a sharpcap and drift method.

[david_taurus83]

I have to set up and remove the kit from the garden each session. So drift aligning is not really an option for me. Would much rather be imaging asap. i use the Polemaster but with the Sharpcap routine. Typical consistent RMS error of around 0.6" to 0.9"

 

I have some longer sessions in those files but I inevitably encountered star losses and PHD spitting its dummy out so the overall error is somewhat skewed. But when all is sailing smoothly, I typically see the above accuracy. I image at 2.33 to 2.65 arc/sec per pixel so its more than good enough for me.

[Dinglem]

This is a good idea for a thread as I usually use Sharpcap as I can't see Polaris through my polar-scope and get pretty good PA. I don't have any results to show because the limited times I get the chance to set up I want to get on with imaging. A couple of sessions ago I'd done my usual Sharpcap polar alignment but because I'd been reading about the new PA tools in PHD2 I thought I'd give it a go and was dissapointed to find it saying my PA was pretty bad, instead of adjusting it I went back to Sharpcap and it said my PA was good, so I left it alone. I'd be really interested if someone far more experienced than me could do a proper comparison and let us know their findings because I'm still at the stage of frustration, why does everything work ok during daylight hours when testing, only for it to get dark and clear then those pesky gremlins come out to play.

[jambouk]

I think it would be relatively easy to polar align in the different ways and then just run PHD2 on either the main scope or the smaller guide scope for 30 minutes and look at the errors for each method of polar aligning (and repeat 3-5 times). It would be a time-consuming project and I guess we know roughly what the data would show (PA accuracy in ascending order: by eye with polar scope < handset polar alignment routine < SharpCap < PoleMaster < drift alignment) but the magnitude of the differences between them would be interesting to know from an academic point of view, especially for the middle three methods. If I knew how PHD2 worked I might be tempted to give it a go from my back garden

[stash_old]

On 05/12/2018 at 20:56, Ronclarke said:

So would I! 

I've been using the polar scope by eye and getting 10 min subs without a problem or buying expensive add-ons.. 

 

Ron

£10 is hardly expensive add on Ron ?

Plus you dont get neck cramps or a dodgy back as you do looking thru a polar scope LOL

All current methods fail anyway --- when there is clouds !

[tooth_dr]

1 hour ago, Dinglem said:

A couple of sessions ago I'd done my usual Sharpcap polar alignment but because I'd been reading about the new PA tools in PHD2 I thought I'd give it a go and was dissapointed to find it saying my PA was pretty bad, instead of adjusting it I went back to Sharpcap and it said my PA was good, so I left it alone.

Funny this was exactly my experience of the two programmes.  I gave PHD2 a brief go at adjusting, but ending up leaving it and back to sharpcap.  I have a feeling that sharpcap might not be that accurate (even through I got it down to 0.01 accuracy)

[Dinglem]

1 hour ago, tooth_dr said:

Funny this was exactly my experience of the two programmes.  I gave PHD2 a brief go at adjusting, but ending up leaving it and back to sharpcap.  I have a feeling that sharpcap might not be that accurate (even through I got it down to 0.01 accuracy)

In that case I may try PHD2 first and see what errors I get when I then try Sharpcap.

[StuartJPP]

I did a back-to-back test of SharpCap and Polemaster a while ago, both produced very similar results which is not surprising as they use very similar methods.

SharpCap's method is based upon PhotoPolarAlign which itself is based upon another that escapes me.

SharpCap has the potential of more accuracy since it can use much longer focal lengths than the 25mm of the Polemaster.

Here were my findings:

 

[Ronclarke]

I was referring to the cost of Polemaster, I don't know what accuracy I get as I use a WiFi dongle not the handset.. Whatever it is, it works foe me.

(I have a 90' camera adaptor fixed to the polar scope to save my back as well!)

 

Cheers

Ron 

[Stub Mandrel]

If you assume Sharpcap's calculation of accuracy is correct, then my alignment with a new-style polarscope is about 17" and using the Sharpcap routine I can get it below 0.5" with no more than patience.

Using the polarscope three-star alignment typically gives me the second and third stars within about 0.1 degree (estimated from camera field of view).

Last time using Sharpcap at better than 0.5" I didn't have to adjust for my second and third stars even after slewing from Altair to Andromeda.

That said, last night I did planetary imaging as an equivalent of 3,600mm with a just polarscope alignment. The planets stayed pretty much centred even over periods of 15 minutes or longer, maybe I was lucky?