Polar alignment and slewing to target

[chubster1302]

OK, what am I missing? Running NINA and Stellarium. Set scope up, did a 3 point alignment in NINA, then switched to Stellarium to slew to Vega to get focus, scope, slewed to right direction but was not centred, in fact wasn't even that close. What am I missing? 

[Steve Ward]

Sounds like the time input was astray , daylight saving missed maybe ... ?

[Budgie1]

8 hours ago, chubster1302 said:

Set scope up, did a 3 point alignment in NINA, then switched to Stellarium to slew to Vega to get focus

When you say "3 point alignment", is this Polar Alignment or 3-star alignment, because they are different things? 

Polar Alignment lines the mount base with the NSP. 3-Star Alignment (normally done on the mount handset) tells the handset where the mount is pointing. If you're using NINA then try using the Plate Solving utility to find your target. It's less time consuming, more accurate than 3-star alignment and you don't need to use Stellarium, although you do need some more downloads of this.  

[chubster1302]

6 hours ago, Steve Ward said:

Sounds like the time input was astray , daylight saving missed maybe ... ?

Hmm....where do I check this 

[chubster1302]

I used Ninas 3 point polar  alignment plug in. I would assume once this was completed I would then be basically bang on when slewing to targets ?

[scotty38]

25 minutes ago, chubster1302 said:

I used Ninas 3 point polar  alignment plug in. I would assume once this was completed I would then be basically bang on when slewing to targets ?

Nope, assuming everything is configured correctly you should not be far off but you'll most likely need to plate solve to be bang on as you say.

When I do it the first slew has the object in the frame but not necessarily centred as I need it.

 

Oh of course this all assumes that the scope is in a known position once TPPA is completed and before the slew. Of course it'll be miles off if the scope is pointing randomly to start with 🙂

Edited June 5, 2023 by scotty38

[Steve Ward]

40 minutes ago, chubster1302 said:

Hmm....where do I check this 

When you are initially setting up the mount ( you haven't specified a mount so I'm assuming a Skywatcher Go-To of one sort or other) you have to input Date , Time etc and there will also be a Timezone and Daylight saving question too. 

As we're now in BST (again assumimg you are in the UK) then you need to press Yes to the Daylight Saving prompt.

Failure to do so will send the scope pointing 15° off your intended target ( 15° /  hour rotation)

[Budgie1]

52 minutes ago, chubster1302 said:

I used Ninas 3 point polar  alignment plug in. I would assume once this was completed I would then be basically bang on when slewing to targets ?

Think of Polar Alignment as the orientation of the mount's RA & DEC axis with the NCP.

Star Alignment or Plate Solving is pointing the telescope itself to the target you want to look at or image.

As Scotty says above, if your telescope starts off from a know position (like the Home Position) then the target will be close when you slew to it. Plate Solving can be used to get it dead centre by taking an image, working out where it's looking and adjusting the position of the mount to centre the target. No looking through EP's or finder scopes to line up with a star or making fine adjustments on the handset. Let NINA do the work for you. 

You can also use the Framing Tool to frame the image if you want it slightly off centre.  

I know it's another thing to get your head around but once you start using Plate Solving you'll realise how much easier it makes things and you'll ask yourself why you didn't start using it earlier!  

[chubster1302]

53 minutes ago, Steve Ward said:

When you are initially setting up the mount ( you haven't specified a mount so I'm assuming a Skywatcher Go-To of one sort or other) you have to input Date , Time etc and there will also be a Timezone and Daylight saving question too. 

As we're now in BST (again assumimg you are in the UK) then you need to press Yes to the Daylight Saving prompt.

Failure to do so will send the scope pointing 15° off your intended target ( 15° /  hour rotation)

Yes, sorry, I have the eg5 Pro. When you say "when you initially setup the mount", is this within NINA?

[chubster1302]

1 hour ago, Steve Ward said:

When you are initially setting up the mount ( you haven't specified a mount so I'm assuming a Skywatcher Go-To of one sort or other) you have to input Date , Time etc and there will also be a Timezone and Daylight saving question too. 

As we're now in BST (again assumimg you are in the UK) then you need to press Yes to the Daylight Saving prompt.

Failure to do so will send the scope pointing 15° off your intended target ( 15° /  hour rotation)

Think the times etc are all ok ? 

[Steve Ward]

4 minutes ago, chubster1302 said:

Yes, sorry, I have the eg5 Pro. When you say "when you initially setup the mount", is this within NINA?

Who's Nina ... 😄

I'm talking about when you first power up the mount , I'm guessing NINA bypasses the common way of aligning for some new-fangled computerised method so I'll bow out of the conversation now and leave it to the whizz-kids to sort you out .... 😏

[scotty38]

Well I see you have the man himself helping you on Discord so you should be getting all the right info 🙂

[StevieDvd]

From your screenshot the LST in Ascom reads the same as your web page does for Greenwich Sidereal Time -  I am assuming that LST is Local Sidereal Time. If that equates to the difference in GMT & DST that could be your issue.

 

[newbie alert]

7 hours ago, chubster1302 said:

I used Ninas 3 point polar  alignment plug in. I would assume once this was completed I would then be basically bang on when slewing to targets ?

Not at all... Polar alignment is to align the mount axis with the pole so its tracking matches the rotation of the earth...

Star alignment is for your pointing , now superseded by platesolving such as platesolve2, ASTAP etc

[chubster1302]

On 05/06/2023 at 12:31, scotty38 said:

 

Oh of course this all assumes that the scope is in a known position once TPPA is completed and before the slew. Of course it'll be miles off if the scope is pointing randomly to start with 🙂

This is the bit I'm getting confused about I think. 

Mount is level and pointing north, using a compass. I even looked in live view of cam and polaris was sitting low in the frame. Then did TPPA in NINA

So, how do I "tell the scope" where it is before I then slew ??

 

 

Edited June 6, 2023 by chubster1302

[Steve Ward]

I would assume that you need to do a Go-To 1,2 or 3 star align before using NINA or any other software to slew to a target.

TPPA is just polar aligning the mount , i.e. making sure that it rotates accurately in relation to the celestial pole , this has nothing to do with pointing accuracy of the Go-to which needs to know ...

1. The starting position of the telescope / mount  , generally the Home position.

2. The location of the mount on the Earth's surface , hence the co-ordinates you input.

3. The time , date , year in order to know what is where in the sky at that particular time in order to be able to slew to a particular object.

The more accurate the infirmation you enter the more accurate that initial slew to target will be . 

[ONIKKINEN]

37 minutes ago, chubster1302 said:

This is the bit I'm getting confused about I think. 

Mount is level and pointing north, using a compass. I even looked in live view of cam and polaris was sitting low in the frame. Then did TPPA in NINA

So, how do I "tell the scope" where it is before I then slew ??

 

 

Have you set up Astap platesolving yet? Once that is done you can auto center targets and can forget about stellarium and star alignments.

[Steve Ward]

29 minutes ago, ONIKKINEN said:

Have you set up Astap platesolving yet? Once that is done you can auto center targets and can forget about stellarium and star alignments.

I understand the basics of plate-solving , well I thought I did , but how does it point the scope in the right place in order to take an image to plate-solve from , or am I missing something here , so please enlighten this dinosaur ... 😆

I assume you have to input the relevant info first as you would to do a basic go-to alignment  without all the added complications that are being suggested , seems like a classic case of being asked to sprint before actually standing up from here ... 😏 

[chubster1302]

34 minutes ago, ONIKKINEN said:

Have you set up Astap platesolving yet? Once that is done you can auto center targets and can forget about stellarium and star alignments.

I've got it set up yes, but haven't been able to fully test, as I had an error, then the clouds rolled in. Hopefully will test tonight. I think im probably over thinking it....so my goal for tonight is...

1. Mount is set up, and pointing North

2. Run TPPA in Nina

3. I'm then going to make sure I'm in focus by slewing to Vega. This is where I would plate solve and get Vega dead centre, correct ?

I think that is basically the procedure, am i correct?

 

 

 

[chubster1302]

7 minutes ago, Steve Ward said:

I understand the basics of plate-solving , well I thought I did , but how does it point the scope in the right place in order to take an image to plate-solve from , or am I missing something here , so please enlighten this dinosaur ... 😆

I assume you have to input the relevant info first as you would to do a basic go-to alignment  without all the added complications that are being suggested , seems like a classic case of being asked to sprint before actually standing up from here ... 😏 

I "believe" it uses an image database held by ASTAP to work it out, it then sends commands through NINA to scope to move in the direction needed, well, thats my very basic understanding 

[Steve Ward]

22 minutes ago, chubster1302 said:

I "believe" it uses an image database held by ASTAP to work it out, it then sends commands through NINA to scope to move in the direction needed, well, thats my very basic understanding 

But how does it get you to the target initially , I understand how it can "tweak" the pointing to centre a target once an initial image is taken but not how it gets to the target in the first place.

Easy enough with planets , Moon  or even M31 , M42 where you can pretty much aim by eye  , but for some 'invisible' narrowband target it must need tht initial alignment ?

[ONIKKINEN]

29 minutes ago, Steve Ward said:

I understand the basics of plate-solving , well I thought I did , but how does it point the scope in the right place in order to take an image to plate-solve from , or am I missing something here , so please enlighten this dinosaur ... 😆

I assume you have to input the relevant info first as you would to do a basic go-to alignment  without all the added complications that are being suggested , seems like a classic case of being asked to sprint before actually standing up from here ... 😏 

There are no added complications, and in fact most of the complications, including "normal" alignment go away.

The first slew will be off but it doesnt matter. An image is taken after the mount communicates to NINA that the slew is complete and then it platesolves. If the mount is no more than a few degrees off, which is usually the case, then the platesolve succeeds in a second or so. The mount is aware of the coordinates it think it is pointing at, and this is the basis for the platesolver where reference stars are searched in a spiral fashion around the reported area. If the mount to sky error is large the search time can be longer. But that will not happen unless there is loss of power or manual movement of the axis (such as bumping the mount).

Astap can platesolve locally with files on disk, and can even blind solve (no mount communicated coordinates, such as with a simple non go-to tracking mount).

[scotty38]

2 hours ago, chubster1302 said:

This is the bit I'm getting confused about I think. 

Mount is level and pointing north, using a compass. I even looked in live view of cam and polaris was sitting low in the frame. Then did TPPA in NINA

So, how do I "tell the scope" where it is before I then slew ??

 

 

Most of the info above gives you what you need but yes TPPA "physically" aligns your mount based on you telling it where you are, time, date etc. .

Once the mount is polar aligned you then need to have the mount start from the known position I mentioned. This is usually the "Home" position pointing at the NCP as you say.

Now we have two things, 1 the mount is physically aligned and 2. The mount "knows" where it is as you have set it to the home position or indeed any position* that you told it about but usually Home/NCP....

Now you can slew to M13, say, and because the mount knows where it is and because it's aligned it just moves however it needs to move to get to the known coordinates of M13. As said above if all is well it'll only be out by a bit and then the plat solving will do the comparisons and move the mount until it's pointing exactly with M13 in the centre.

Hope that ll makes sense, it did to me at least and also as you know you can do all of this in NINA BUT you do need ASTAP setting up with its database and you also need to tell NINA to use ASTAP for solving.

 

*GSServer for example can be configured with various positions, in fact the "Home" position can be anywhere but GSS knows this so knows where it is and therefore where it needs to go to get to the object that's been asked about. I'm not quite sure about EQMOD and that "may" need you to start from the typical home position.

Edited June 6, 2023 by scotty38

[ONIKKINEN]

38 minutes ago, chubster1302 said:

I've got it set up yes, but haven't been able to fully test, as I had an error, then the clouds rolled in. Hopefully will test tonight. I think im probably over thinking it....so my goal for tonight is...

1. Mount is set up, and pointing North

2. Run TPPA in Nina

3. I'm then going to make sure I'm in focus by slewing to Vega. This is where I would plate solve and get Vega dead centre, correct ?

I think that is basically the procedure, am i correct?

 

 

 

1,2, sounds good.

3) Yes, sounds about right. You can slew to vega from the manual focus stars list (or externally from stellarium but i dont recommend it, its just an extra step with little benefit).

Once the slew is complete you will likely see that Vega is not in the frame. Hop on to the platesolve tab and run it with re-slew and sync options turned on and then it will take an image, platesolve, re-slew, rinse and repeat untill within tolerance. Word of warning here, some mounts dont like the sync option and you can leave it off if you notice something weird.

Edited June 6, 2023 by ONIKKINEN

[Steve Ward]

3 minutes ago, ONIKKINEN said:

The first slew will be off but it doesnt matter.

So you just point the 'scope anywhere , take a snap , the software recognises the part of the sky and then slews to the correct position ... ?