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Old 19-10-2020, 06:53 PM
Craig_
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Join Date: May 2020
Location: Sydney
Posts: 307
Quote:
Originally Posted by The_bluester View Post
You can sync near the pole (As it is unlikely you will be pointed exactly at the pole) but it is not a good idea as it is error prone. As Steve pointed out, if you are pointed directly at the pole RA is undefined. If you plate solve at the pole and the plate solve result is on the opposite side of the meridian from where EQMOD assumed the scope was it will reject the sync. That one tripped me up getting meridian flips automated at one point due to cone error, after the flip the telescope was pointed just a few minutes east of the meridian and it would fail there. Delaying the flip an extra ten minutes solved it.

Make sure your polar alignment is good, then the park position is reasonably accurate and do your first goto. Then polatesolve and sync. Or even just randomly point off to the east somewhere and plate solve/sync will do, just get away from the pole and meridian.

It was mentioned above about syncing multiple points which builds a pointing model. I Know APT recommends working that way and when I was using APT I had a routine down which captured maybe ten sync points each side of the meridian (Append on sync) before I would start imaging after which gotos were quite accurate, but it still usually took more than one pointing iteration to get right on target.

SGP and Voyager (Which I use now) use a different routine, the sync there in EQMOD speak is "Dialog based" What it does is realign the whole pointing model on the one sync point. I can't recall how SGP does it precisely so I will only mention Voyager here. When you request a precise pointing operation, it issues a goto and when that finishes, it plate solves and syncs the mount, if it has missed the target by more than your defined value, it issues another goto (Much smaller now) and then plate solves again, iterating in typically smaller and smaller steps until it hits the threshold for accuracy. Even with my AZEQ6, it generally took no more than three iterations to be within the limits.

I prefer the dialog based sync, while it is cool to see accurate gotos first time after building the pointing model it had to be done every night.
Thanks heaps for the info. I think your first paragraph probably answers the challenge of why EQMOD rejects my sync near the pole. With respect to your second paragraph:

Make sure your polar alignment is good, then the park position is reasonably accurate and do your first goto. Then polatesolve and sync. Or even just randomly point off to the east somewhere and plate solve/sync will do, just get away from the pole and meridian.

This is, more or less, what I do now. My challenge is that very often after I slew away from the pole, the platesolve fails for reasons unknown - all settings are configured correctly (demonstrated by the successful platesolve at the pole!)

The building of the sync points to improve accuracy makes sense, although for now GOTO accuracy is not so much my primary concern as being able to sync to begin with



Quote:
Originally Posted by jahnpahwa View Post
Hmmm.... so once I've done the 90deg RA turn for sharpcap, I slew roughly back to the SCP and hit another PS (I always do auto PS, using the planewave set of point data). I think it actually auto syncs everytime you PS. I hit sync manually each time too. It may be a rubbish synch, but its not far to rigel kent, and my understanding is the auto platesolve solves in a spiral out from where it thinks it should be, so that first solve away from the pole usually takes from 10 to 70 seconds... but usually under 25. I wish I knew of the trick I'm doing! If its not working for you, I'd give it a slight kink in Dec when slewing back after PA, just tohrow it off the smallest amount, and that will give it something to chew on and develop a model around.


The other back to basics thing is, how precise are you with levelling your mount? I was using an app for spirit level, but am now using a little clear spririt cube thing, and get things super level. In my mind, being out of level could make it harder for that first solve, and again, going a long way from home will open up that gap wider and wider if your mount is half a degree skewy.



Overall, I think a little move from the pole first up might help, and see that this is also being mentioned by others
Thanks for the info! In this sentence "Hmmm.... so once I've done the 90deg RA turn for sharpcap, I slew roughly back to the SCP and hit another PS (I always do auto PS, using the planewave set of point data)." What do you mean by planewave data sorry?

"so that first solve away from the pole usually takes from 10 to 70 seconds... but usually under 25."

Yeah this one has been a mixed bag for me. PS at the pole is usually 3-10s depending on whether I use ASPS or PS2 (ASPS is faster IME) but away from the pole can take 30 seconds or so. I've tried blind solving and can be waiting minutes for no result sometimes.

"If its not working for you, I'd give it a slight kink in Dec when slewing back after PA, just tohrow it off the smallest amount, and that will give it something to chew on and develop a model around."

Interesting, I will try that, thanks!

"The other back to basics thing is, how precise are you with levelling your mount? I was using an app for spirit level, but am now using a little clear spririt cube thing, and get things super level. In my mind, being out of level could make it harder for that first solve, and again, going a long way from home will open up that gap wider and wider if your mount is half a degree skewy. "

I'd like to think I am fairly accurate, I do put the time in to do it right and use a physical spirit level like you mention with a dual-axis bubble.

Would I be correct in saying that from the pole, where I can always successfully PS, the further away from the pole I slew for my initial first PS+Sync, the less likely the chance is for it to work? I should try and only move a little away?
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