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Meade LXD-75 Alignment question

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#1 Charles Hall

Charles Hall


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Posted 02 April 2011 - 06:55 AM

I'm setting up my LXD-75 in a more or less permanent location, so I'm trying to get the polar alignment close to right.

I've noticed that after the handbox says "Successful alignment" I get a screen like this:

69'^ 33'>

I thought this might be telling me how far off my polar alignment was, so I twisted the mount a fraction of an inch and started over. This time I got:

8'^ 8'>

So I have two questions. (1) Is this display telling me what I think it is?, and (2) How accurate should I hope to get it? If it's really within 8 minutes of where it should be, that would seem to be really good (too good!).


#2 rutherfordt



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Posted 02 April 2011 - 07:50 AM


That is exactly what it is telling you-- sometimes you get lucky. :-)


#3 avarakin


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Posted 03 April 2011 - 01:20 AM

Your objective is to get message "alignment error less that 5' "
It is reasonably easy to achieve such alignment using Kokhab method.


#4 Eddgie



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Posted 03 April 2011 - 10:30 AM

I just want to point out that it is not that important to get the numbers smaller unless you image, in which case, you want them to be ZERO.

But if you are using the scope visually only, then it doesn't matter, and you may be wasting your time doing a re-alignment.

The Go-To performnace won't necessarily be any better if you take the time to re-align. The computer in the scope uses the alignment numbers to know how much compensation it needs to put in when it moves to the next target. The numbers can be very large, and the scope will still know where to point to put the next target into the field.

The only advantage (for visual use) of makeing the numbers smaller is that most Go-To mounts only TRACK in Right Ascension. After the mount slews to the target, the Dec motor doesn't turn any more. Only the RA motor turns.

If the alignment is really far off, what happens is that over a period of (usually) many minutes, the target can drift out of the center of the field because it is only tracking on one axis.

If you were doing planetary observing at very high powers (300x to 400x) this drift can be fairly fast, but for 100x to 200x, it takes much longer for a planet to drift out of the field (though you want to keep int somewhat near the center, though a touch of the control button is usually enough to tweak it back in).

So, it isn't necessary to re-align the mount every time to attempt to improve these numbers. Mostly, you are just wasting your time.

And if you were imageing, you would want to do a polar alight routine anyway.

So, don't kill yourself trying to make these numbers smaller and smaller. For most visual observing, it doesn't matter. The scope will still locate the target and put it in the field on the initial slew even if the numbers are not all that small.

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