Polar Alignment using APT and blind plate solving

[Dilsh]

Hi all,

I had a question about polar alignment.

I am very much a beginner and I do not even have a mount as yet (
I am still waiting for Eq6r-pro stock.)

Was reading about plate solving in APT, mainly in the context of 'star aligning' the scope.

The process for aligning to scope in APT seems to be
1) Polar align the scope
2) Slew the scope somewhere random away from the SCP and start tracking
3) run Point Craft and blind solve for this position and then sync with the mount (analogous with a one star alignement)
4) goto++ for desired imaging object.

I was wondering for polar alignment if these steps would work
1) roughly align scope to SCP
2) run blind plate solve
3) move alt-az based on results
4) redo above two steps till polar aligned.

Am I missing something here (i feel like I most certainly am) or can this work for polar alignment.

Cheers
D

[Merlin66]

D,
Sounds pretty good.
I’ d suggest keeping things simple and recommend SharpCap (the freeware version works well V2.9) for the PAalignment.
Then move onto the slew and PS solve etc.

[Dilsh]

Hi Ken,

Thanks for the advice. I'm trying to find v2.9 but it looks like only 3.1 is available on the website. Will probably just pay for the license if I find it useful.

Thanks again,

D

[Merlin66]

D,
I still use V2.9, but the V3.0 seems to be the same....
https://www.sharpcap.co.uk/sharpcap/sharpcap/downloads/sharpcap-3-0-downloads

[jahnpahwa]

Kind of sounds like you're effectively using your imaging scope as a polar scope, and platesolving to bring the pole to centre. The issue that I can imagine is that you're not getting feedback on the adjustments that you're making, and I can imagine many, many, many iterations to get sort of close.

Like Ken says, sharpcap is great for this. You go through a 1min RA rotation procedure and once done it gives constant feedback on your adjustments to alt and az, its doing a similar thing, solving continuously as you adjust. This method brings PA to under 15 arc seconds on each axis within a minute or two. And the final adjustments to get it to that level must be less than 1/100th of a turn of the alt and az knobs. Often the last 10 seconds of adjustment is just tightening one knob "a bit harder" against a stop that is not moving.... its very precise!


Your idea shows that you have the concept of it on lock, which is a good sign. (and reading APT doco before your mount arrives, to boot!)

[Dilsh]

Hey Ken,

Thanks for the link. I'll try it out.

I get your point JP. It would probably take many iterations to get it right. It is interesting that APT does not include this as a feature. Supporting the guy that wrote Sharpcap seems like the right thing to do. As I cannot get the EQ6R PRO all I can do is read manuals :P.

As always, thanks for the help guys.

Cheers,
D

[Wilsil]

I tried SharpCap 2.9 for the first time last Saturday and failed.
The camera couldn't find enough stars to solve.
I am using a DSLR what works after I installed the ASCOM driver for DSLR. SC only saw 6-8 stars.
I think that the exposure time was not long enough, will have to try again after increasing the exposure.

[Merlin66]

Wilco,
I use an eFinder - a 60/230 finder with the DMK51 camera.
I use this to check the PA using SharpCap, usually plenty of stars available.

[Wilsil]

I had it working once.
After increasing the ISO and exposure time, it solved the first picture.
When moving the mount 90 degrees as stated, Sharpcap crashed.
I can't get pass the first solving.
Error message was "Exception Type: ASCOM.NotConnectedException"

[JimsShed]

If you use the polar alignment feature in Sharpcap, it does what you're after re plate solving and in real time tells you which way to adjust your mount. Just brilliant.

[Wilsil]

Finally got Sharpcap 2.9 working last Saturday night.
The error I had previously was I think because the camera was being accessed by Sharpcap and APT at the same time.

Another thing I noticed is that you have to be already positioned pretty good before it plate solves. If it takes too long to plate solve the first image, it means that you are pointing more then the minimum degrees required away from SGP.

[JimsShed]

Yes you are correct on both points re camera connections and initial PA error.
If you have a scope with a long focal length like an SCT and are too far away from the SCP, then you may want to do an initial PA through your guide scope, then do it again through the imaging scope.

When doing the left/right up/down adjustments I don't even look at the image anymore, I set my camera for 4 second exposures and just focus on the Polar Align Error Results at the bottom of the screen.

[Wilsil]

Focal length isn't long, 600mm with the ED80, same scope as yours according your signature.
What I noticed with those error numbers, you keep turning and suddenly they seem to freeze, then go again.