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Improving PA and GOTO - the easy way?


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While being eaten alive by the mozzies last night.....I found the alignment of my NEQ6 was a bit out and the GOTO accuracy marginal...
Then it came to me -
Assumptions:
1. Your time and location have been correctly and acurately entered into the Syscan (I'm still using V3.27)
2. You're happy with the SW capabilities - ie GOTO accuracy about one arc min.
3. Any "cone" error has been corrected. See SW Manual.
4. The mounting is "roughly" aligned to the pole.
 
Ok......
a. Connect the handcontroller to your PC (or use EQmod) and open your planetarium package (I use CdC).
b. Connect to your mount and make sure all the normal movement functions are operating.
c. Set the scope up to get a known bright star in the middle of the FOV (you can start by using the finder cross-wires).
d. Find the same star on CdC and "sync" to this star.
e. Then, using the CdC screen, locate another bright star - start with whatever is available....
f. Use the CdC "Slew" command to move the telescope to the second star.
Check the finder/ FOV to locate the target star -
g. Now, USING ONLY THE ALT/AZ adjusting bolts (Don't touch the RA/Dec) move the mount to bring the target star central.
h. Check by slewing back to the first star - repeat e/f/g above as necessary (usually not!)

That's it - I feel this method is a bit like extreme drift alignment.
The first slew uses the location/time and sky cordinates to move the scope - if we were in perfect registration with the sky it would land on the target..by moving the mount in Alt/Az we are re-aligning the mount's axis to the sky...

Let me know what you think.
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OK, you set up every night and need to get decent polar alignment. Again, start by defining what is acceptable. The answer lies in your field rotation acceptance, nothing else. You may be surprised to

James, The method uses the inherent abilities of the GOTO function....doesn't rely on any special accuracy other than the built in stepper pulse rate. When you GOTO the second star, the mount is inter

A guess would be that you should get it to 10 arc-minutes or so. I ran my remote obs on just under a degree of PA error for a few mounts due to misaligned holes in the pier... Round stars but serious

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Hmmmm... I'm not able to comment technically, so for all I know it might be the best method ever. Sounds similar to the 'Alignmaster' type method though, so must a grain of logic or two in there.

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That's essentially what the SS3k method is, although it won't let. You sync unless you have three good, widely separated points.if you only have one, for a polar aligned mount,I can't see any reason this won't work.

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Thanks guys!

Think of it as registering a piece of graph paper with a similar transparent graph paper overlay ( both in RA/ Dec)

One is the "actual" sky and the other the "mis-aligned" mounting...

We have one fixed point ( the original "sync" star) and by using another distant star can determine how much the "transparent" overlay has to be rotated (in Alt/Az) to bring them into align.

Much easier than three star alignment etc etc - which can still show errors....

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Wouldn't (h) automatically fail?

You have moved the direction the mount is pointing at (g) without the electronics knowing, so when it slews back to the original target star I cannot see how it would take this manual adjustment into account.

My other problem is I do not have a PC/laptop to use outside.

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Yeah. But the polar alignment error value I get from the Synscan handset is less than the error I see through the eyepiece when star aligning, or when slewing between objects for that matter. This seems to negate your method, unless I misunderstand what you're suggesting. In other words what I'm saying is that the error you see when doing a star alignment is not only due to your mount's polar misalignment.

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I don't believe the data the handset gives on the mel and maz errors as i think they rely on too many variables. I've found my tracking doesn't relate to the size of the numbers.

James

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Well, I've just had another go at a form of drift aligning, and once Id done that (and re-booted by AZEQ6), and then done a really precise 3 star alignment with a 12mm reticle eye piece, these were the errors I got:

And now I am managing to get 120 second subs of M57 with my 180mm Mak (2700mm focal length). They look ok on the DSLR LCD, but we'll see what they look like on the PC when stacked, as long as the wind doesn't blow my kit over :)

James

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Edited by jambouk
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OK. I get Mel and Maz errors of between about 5' and 10' with a standard polar alignment without drift alignment. So your results on this occasion rather suggest that the error claimed by the handset is meaningful.

It would be interesting to misalign the polar alignment by a known amount, and then do another 3 star alignment to see if they correspond with one another. The cross in the middle of the polar telescope reticule circle is close to 44.5' from Polaris isn't it.

Edited by Ouroboros
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Interestingly, and I turned the mount off twice and did a 3 star alignment twice, after the 3 star alignment, on this occasion it said "alignment poor", which is something I've never seen before, but the GOTO has never been as good as it is tonight.

With regards your idea Ouroboros yes, it would be interesting, but at the end of the day, I think which is important is how long one can image for without getting trailing, irrespective of what those numbers say.

James

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You're right certainly. I've only had my AZ-EQ6 and GOTO a few weeks and so I am still finding my way with it. I am rather hoping that with guiding, drift alignment won't be necessary. That certainly seems to be my experience so far.

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Guiding with poor alignment will give guide corrections in both RA/Dec and probably field rotation.

The better the alignment, the better the guiding....

Guys,

Give this method a go the next time you have the chance, and compare the results with other methods you use.....

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I only use the handset, I don't connect my mount to the laptop.

I'm not convinced my GOTO accuracy is good enough to meet your criteria.

But maybe I'll have a go. Clearish nights are just a rarity, especially when I'm off the next day!

James

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James,

The method uses the inherent abilities of the GOTO function....doesn't rely on any special accuracy other than the built in stepper pulse rate.

When you GOTO the second star, the mount is interpreting the difference in the RA/Dec given by the planetarium program and issues the "correct" number of pulses to each axis.

The final difference is caused by the mis-alignment of the mount axis to the sky...

By relocating the target star back to the centre using Alt/Az corrections, you are correcting this mis-alignment.

Subsequent GOTO's should be more precise, but always limited by the stepper pulses of the mount.

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I hope it's OK to copy the instructions here.

"11.3 Polar Alignment without Polar Scope

The polar alignment function can help users to polar align an equatorial mount accurately.

Here are the operating instructions:

1. Complete a 2-star alignment or a 3-star alignment. At the end of the alignment, the Syn- Scan hand controller will display the polar alignment error (refer to Section 3.3). Users can use the data to determine whether it is necessary to adjust the polar alignment.

2. Press the “SETUP” shortcut key, and then access to sub-menu “Alignment\Polar Align. >”, press the ENTER key to proceed to the next step.

3. The screen will display “Select a Star”.

• Use the scroll keys to browse through a list of star names and press the ENTER key to

pick one as the reference star for polar alignment.

• The mount will start slewing to point the telescope to the reference star.

4. Use the direction keys to center the reference star in the eyepiece of the telescope after the mount stops slewing. Remember to end the centering operation with Up and Right direction keys. Press the ENTER key to proceed to the next step.

5. The screen will now display the polar alignment error again. “Mel” is the error in altitude and “Maz” is the error in azimuth. Users can refer to these data to estimate the amount of the adjustment to the azimuth and latitude of the mount in the next step. Press the ENTER key again to proceed to the next step.

6. The mount will slew to a new position. When it stops, the screen will display “Adjust Az/ Lat:”. By using the azimuth/latitude adjustment mechanisms of the mount (not using the direction keys on the hand controller), the user should center the reference star in the finder scope, and then center the star in the telescope’s eyepiece. Press the ENTER key to confirm the centering operation.

7. Go back to the “Alignment” menu on the SynScan hand controller and execute another 2-Star or 3-Star alignment, and then check the polar alignment error data reported at the end of the 2-star alignment or 3-star alignment. Repeat Step 2 to Step 7 until the error is small enough and acceptable. Generally, users can get up to 1 arc-minute polar align- ment accuracy after repeating this polar alignment process 2 or 3."

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