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GOTO - I wish really need help !!!


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I'm sure its obvious ?, sorry if the post is a bit long but I need to get to the bottom of this. Kit used is in signature.

So i set up my kit and am very care full about the order

1 - Polar align the mount

2 - Mount the scope and various accessories

3 - Polar align again

4 - perform a 2 star alignment

Then when I use goto the object is never in the centre of the view finder - using a 25m EP and I have to move the scope via the handset to get the target into the FOV and centre it, very often the the object is not even in the FOV of the Finder Scope

When I park the scope it always goes to the correct home position.

Whilst I can normally adjust the via the handset to find the target this is obviously no good when imaging something that cant be seen ?

I am guided but using the above setup process I can get 3 mins exposures with no issue.

Last night I followed the procedure and made the following observations

1 - Polar align - went fine

2 - Mount the scope and various accessories - went fine

3 - Polar align again - went fine

4 - perform a 2 star alignment

my first star was Caph and the scope slewed and i could see the star in the Finder scope so centered and then went to

Arcturus and again it was in the Finder Scope so I centered and alignment was complete.

I then went to Altair, scope was pointing in the right direction but I had to adjust to get it in the Finderscope, sorry can remember by how much but it was the left arrow on the handset, i then tried to goto M27 and the same thing again.

So I parked the scope and started over

This time I align firstly on Altair, scope moves and the star is not in the finder scope so I find it and center it, then went off to Arcturus same story. Then I went to M27 and i could clearly see it through the 25m EP not centred but right on the left hand side.

Hope the above makes some sense, its really frustrating and I'm not sure were I'm going wrong ?

I have included the instructions below that I use for Polar aligning

1. Look through the polarscope and rotate the RA axis until the 'Polaris' circle is right at the bottom.

2. Keeping the RA axis still, spin the RA setting circle round until the zero point is next to the triangular index mark.

(What you're doing here is setting the mount up so that when Polaris is at its highest point in the sky, the RA setting circle reads zero. [Recall that your polarscope shows the sky inverted, so when Polaris is really at its highest point, you want it at the bottom point in your scope]. NB You probably only need to do these first two steps once, as long as you then leave the RA setting circle alone.)

3. Read the first number from the handset's display. In this example we know that it is 20 hours and 45 minutes since Polaris was at its highest point. As we now have Polaris's highest point associated with zero on the RA ring, we just rotate the RA axis until the setting circle shows 20:45 next to the index mark. IMPORTANT: In the northern hemisphere, you use the upper set of numbers on the scale.

4. Look through the polarscope - the 'Polaris' circle is now down at the bottom-left - in the 7:37 position - exactly the right place for polar alignment. Use the altitude and azimuth screws on the mount to place Polaris in this circle and you are now polar aligned. Voila!

Regards

John B

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Not sure that my ramblings wll help you, but hopefully they will make sense!

It sounds as though your polar alignment routine is fine. So, onto your mount alignment. I always do a 2 star alignment and it works well. From SGL I have learnt that it is best to use a star in the south (Currently for me Antares) and then one near to where you are looking at targeting for the evening (At the moment Deneb).

On the first star alignment, my star is rarely in view, so I manually get it central in the viewfinder (in my case my camera connected to the scope) unlocking the RA and DEC clutches and then relocking when central. For the second star alignment, it's always nearly there, and so I adjust a little with the handset. Voila!!

Just a thought, have you ensured that the finderscope and telescope are lined up correctly? It could be that while you are using your finderscope for alignment, it doesn't marry up exactly to what you see from your scope. You can align this in daylight looking at a distant object.

Also, I have just updated my firmware in my handset, it has made a noticeable difference to the accuracy of my alignment.

Edited by swag72
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I allways ensure that the finderscope is lined up

I will take on board the stars to use when aligning thanks

I will check to see if my handset is up todate (is there a website for that with clear instructions) , its all so frustrating.

John B

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Hi John,

Assuming for now that your polar alignment is correct, on the FIRST star, don't move the telescope using the remote handcontroller to align on it, unlock both the RA and DEC clutches and physically push/pull the telescope until the FIRST star is in the centre of the FOV. Lock the clutches and then accept the alignment on the handcontroller. For the second star, use the handcontroller to centre it.

This will fool the system into believing that you had started from a perfect 'HOME/PARK' position as this is critical to the success of this GoTo system.

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FIRST star, don't move the telescope using the remote handcontroller to align on it, unlock both the RA and DEC clutches and physically push/pull the telescope until the FIRST star is in the centre of the FOV

Interesting, of course your direction prompts a question. When You start the process it asks for a star and slews to it, i assume that when you manually adjust the scope ?

John B

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On your first star, after the scope has slewed to it and if it's not central - Manually get it central in your viewfinder with the DEC and RA clutches as already stated.

Edited by swag72
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Also make sure that you are aligning to the correct star.

One evening a few years ago, I was selecting Caster on the handset and aligning to Pollox - took me a whole evening to work that one out :smiley:

Ant

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Fair question but im sure im getting the right star, and the problem has been ongoing for a while, its only become an issue now as Im trying to image things that I cant see (hope that makes sense)

John B

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Don't know if this is any use with your mount but it works like a charm with my AP. I also seem to remember doing this with my G11 when I used to set up each night.

Make sure your handset is correctly set up in respect of Lat/Long and time.

First, I never Park the mount in the accepted sense. I simply switch off, slacken the clutches and then lower the scope so I can shut the roof. I then put the scope in a 'comfortable' position and lock up.

So, first thing is to open the roof and I have to lower the scope to do that. Polar alignment is not lost as the mount is on a pier.

Second job; point the scope at a known star, ideally near my centre of interest for that night. Set focus mode on the camera and centre the star (or use an eyepiece).

Tell the handset what star the scope is pointing at, ie; Synchronise the scope to the sky. That's it.

If I move to a star a long way from the first star the mount might lose synch slightly. I don't care as a re-cal, once centred on the new star, takes about four seconds.

I have never fully understood the need for multi star alignment as your mount handset knows how many ticks of the encoder it takes to go from A to B. Therefore your alignment should be accurate no matter how many stars you use.

Just use one star, close to your object of choice.

Synchronise on it.

GoTo your object of choice.

Re-Cal (not really necessary)

Take pictures.

Dennis

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I have never fully understood the need for multi star alignment as your mount handset knows how many ticks of the encoder it takes to go from A to B. Therefore your alignment should be accurate no matter how many stars you use.

This is for counteracting the effects of 'cone error'. Obviously, getting rid of cone error at source is a better option but not always easy to do.

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  • 2 weeks later...

i dont even do a star alignment after polar aligning....if i have a target for the night to image then i polar align............find the nearest bright star to my target......slew to it and then re-centre it in the reticule(sharpcap) and then just move to the object im imaging ............works near perfect every time

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