Polar alignment and slewing to target

[adyj1]

1 hour 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 ??

 

 

In a nutshell, what you are trying to do is make sure the 'telescope control software' - which in your case is EQMod - knows where the mount (and therefore your scope) is actually pointing. EQMOD doesn't actually know when you first power up... 

EQMod 'assumes' by default that your mount is pointing North, weights down . Your job when setting up is to release the clutches and physically point your mount north, so that it is pointing where EQMOD thinks it is. Now everything is in harmony and you can tell the mount to slew to a target.

When it slews it will never be 100% accurate - because our mounts are built to a budget - and so you do a platesolve to resync the location that EQMOD *thinks* the scope is pointing at and where it is *actually* pointing. After the sync, the mount can be given the same slew command as before, and will point more closely (hopefully exactly) at the intended target. This may take 2 or 3 slews.

When you do a 'plate-solve' you are actually doing a very, very accurate one-star alignment. ASTAP looks at the picture which your camera took and works out from the stars and your field of view where *exactly* your mount is really pointing - and tells EQMOD the exact location by 'syncing'. 

Hope this helps...

Ady

[ONIKKINEN]

2 minutes ago, Steve Ward said:

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 ... ?

Yes, thats the gist of it. It really is that simple.

[Steve Ward]

4 minutes ago, ONIKKINEN said:

Yes, thats the gist of it. It really is that simple.

That's witchcraft not 'simple' ...  

I'll stick with solar for the time being , it's easier to find ... 😆

[chubster1302]

12 minutes ago, adyj1 said:

In a nutshell, what you are trying to do is make sure the 'telescope control software' - which in your case is EQMod - knows where the mount (and therefore your scope) is actually pointing. EQMOD doesn't actually know when you first power up... 

EQMod 'assumes' by default that your mount is pointing North, weights down . Your job when setting up is to release the clutches and physically point your mount north, so that it is pointing where EQMOD thinks it is. Now everything is in harmony and you can tell the mount to slew to a target.

When it slews it will never be 100% accurate - because our mounts are built to a budget - and so you do a platesolve to resync the location that EQMOD *thinks* the scope is pointing at and where it is *actually* pointing. After the sync, the mount can be given the same slew command as before, and will point more closely (hopefully exactly) at the intended target. This may take 2 or 3 slews.

When you do a 'plate-solve' you are actually doing a very, very accurate one-star alignment. ASTAP looks at the picture which your camera took and works out from the stars and your field of view where *exactly* your mount is really pointing - and tells EQMOD the exact location by 'syncing'. 

Hope this helps...

Ady

OK, cool. So i think ive been doing it right but overthinking it. Mount is pointing North, weights down, scope in line.....so switch on and connect and I should be "good to go". There is nothing to set in EQMOD or NINA so to speak?

[adyj1]

49 minutes ago, chubster1302 said:

OK, cool. So i think ive been doing it right but overthinking it. Mount is pointing North, weights down, scope in line.....so switch on and connect and I should be "good to go". There is nothing to set in EQMOD or NINA so to speak?

Nina will take the scope location from EQMOD, so it's just the pointing North bit. 

If things go really awry, use Nina to target polaris. (be prepared to loosen off the clutches while it is slewing if things are really out of kilter.) Once it stops, you know where EQMOD thinks it is, so manually point the scope north and tighten the clutches. 

EQMOD is what all other software (Nina, Stellarium, CdC etc) refers to for where the scope is pointing. Plate-solving is used to keep EQMOD accurate after a slew. 

Added:

Oh, and plate-solving has a built-in tolerance. If it thinks the scope is wildly out it won't sync. 

Edited June 6, 2023 by adyj1
Added

[chubster1302]

28 minutes ago, adyj1 said:

 

Added:

Oh, and plate-solving has a built-in tolerance. If it thinks the scope is wildly out it won't sync. 

Perfect thanks...

As for the quoted text. I believe the error I got was "telescope out of tolerance" so assume that is why I was getting that 

[Budgie1]

A little tip which may help.

If you haven't done so already then set the mount's Home Position.

• Firstly, in EQMOD, press the "Park to Home Position" button at the bottom of the main page and let the mount slew to it's Home Position.
• Now check that the Home Position is set correctly - Here's a video showing how to do this if you're not familiar with the process: How To Set The Equatorial Home Position
• Once the Home Position has been set correctly, use a Sharpie to mark the body of the mount on the RA & DEC axis, so you can easily put the mount back into it's Home Position if you release the clutches.

Now, if the clutches slip or the mount gets knocked, it doesn't matter because you can simply tell EQMOD to put the mount in it's Home Position and then release the clutches to manually put the RA & DEC axis on their marks and you know it's in the correct Home Position every time.  

[newbie alert]

On 06/06/2023 at 15:21, 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 ??

 

 

The known position would be home position, IE weights down pointing at the NCP

Pointing with a compass is magnetic north, not far from the NCP but not quite accurate

To polar align the mount doesn't need to be level

[adyj1]

53 minutes ago, newbie alert said:

To polar align the mount doesn't need to be level

Although if you have a goto mount and are using software like Nina's polar alignment plugin, being close to level is useful for PA (because your axes align with the adjustment instructions of north/south east/west) 

[newbie alert]

9 hours ago, adyj1 said:

Although if you have a goto mount and are using software like Nina's polar alignment plugin, being close to level is useful for PA (because your axes align with the adjustment instructions of north/south east/west) 

So when you adjust the alt az bolts on polar alignment aren't you doing that anyway??

IE aligning the axis 

Edited June 8, 2023 by newbie alert
Added info

[adyj1]

2 hours ago, newbie alert said:

So when you adjust the alt az bolts on polar alignment aren't you doing that anyway??

IE aligning the axis 

To put it simply, if you have a level mount your alt bolt will go straight up and down. If the mount isn't level , it will go "up and a bit to the right" or "down and a bit to the left" (depending on how badly out of level the mount is).

Not the end of the world, for sure - and once PA has been achieved there is indeed no difference at all as to whether the mount is level - but when you are adjusting one axis on your mount and it is changing both axes in your software, it can get a little frustrating... (hence me saying 'useful' to have a fairly level mount).

 

[newbie alert]

10 hours ago, adyj1 said:

To put it simply, if you have a level mount your alt bolt will go straight up and down. If the mount isn't level , it will go "up and a bit to the right" or "down and a bit to the left" (depending on how badly out of level the mount is).

So during the polar alignment process if you dont align the axis then the software won't align the other stars as they're be abit down right or up left... Whichever method you choose other than a simple polar scope method with either align other stars or show drift up/ down, left or right or as you put it north,south east or west.. 

[nickarp2000]

It's a little different with my set up using my Cem60. Once I have polar aligned using the i-polar, I must use this position and tell the mount it's the new Zero position in the handcontroller. From there I open nina and go to my manual focus tab and just select the first star in the list. Mount goes there but doesn't use ASTAP for plate solving at this stage. I then manually focus to get the best star image I can by imaging in 5 second bursts. From that point I use Stellarium to pick an object. From Stellarium back to Nina and open the framing tab. Get coordinates from Stellarium and then slew and centre. Plate solving now works because my focus is good enough for it to recognise the star field patterns the camera images. If I'm not close enough to focus I can't plate solve. I can the keep in the framing wizard and play about with the box around the object until I'm happy with the position in the frame. 

From there off to sequencing and set up the lights darks etc. Tweek focus and off we go. 

Nick

 

 

[adyj1]

2 hours ago, newbie alert said:

So during the polar alignment process if you dont align the axis then the software won't align the other stars as they're be abit down right or up left... Whichever method you choose other than a simple polar scope method with either align other stars or show drift up/ down, left or right or as you put it north,south east or west.. 

I used the term 'align the axis' and in hindsight it is not a good description... 

Polar alignment is making the rotation point of your mount's RA axis point precisely at the point in the sky which is the Celestial Pole (very close to polaris). Once you are polar aligned it doesn't matter if your mount is level or not - you are polar aligned. 

When I said 'align the axis' I meant that on a level mount, when you adjust the altitude bolt the mount will move strictly up or down, and not at all left or right. Similarly, the azimuth bolt will move the mount left and right and not at all up and down. 

If your mount isn't level, when your PA software tells you to adjust a certain amount north and another amount west, you find yourself making the necessary altitude adjustment north, but when you start making the west adjustment it slightly changes the north alignment as well, meaning you have to go back to your Alt adjustment to tweak north/ south again...

Sure you can alternate to get them closer and closer until you are accurately polar aligned, but its nice to be able to do it without a lot of backwards and forwards adjustments between Alt and AZ. 

But at the end of the day, PA is PA, and if you get acceptable results - level or not level - that's a win.