LX-200 pointing trouble - long format better ?

Oliver Kloes Feb 29, 2004

Hi Lawrence, hi Bill,

would using the "long format" of the LX200 (RA and DEC minutes and seconds
transmitted as MM.SS, short format uses MM.M only) improve the pointing
accuracy of Lawrence's scope?
(please note: only the newer ones of the Classic LX200 with "High precision
pointing" have this option)

Unfortunately with every shut down of the LX200, "short format" is set as
default and there is no way of setting "long format" with the key pad - as
far as I know. Great programming by MEADE!! ;-(

So I have to use a LX200 control software or hyper terminal to send the
LX200-command U#
to toggle the formats.

GUIDE recognize the format since an update of version 7.0 already. It's
noted at line 49 of starup.mar.

One suggestion for a improvement of the LX200 telescope dialog:
If the telescope is set for "short", a window opens "LX200 set to short
format. For better position accuracy set to long format?""with a button to
send the command U#
Could this be done?

Lawrence, at startup.mar you'll find the following line:

49 lx delay 15 400 9600 0 2400

The 0 between 9600 and 2400 indicates the LX200 sends its position in "short
format", if there is a 1, it uses "long format"

Clear skies,

Oliver



> >Subject: Re: LX-200 pointing trouble
> >
> >Hi Lawrence,
> >
> > Hmmmm... just how much error are we looking at here? A few
arcminutes?
> >Dozens? Degrees? I assume the error is repeatable (i.e., go from one
> >part of the sky to another and back again, and it's still off in the
> >same direction by the same amount)? Any clues other than "it's off"?
>
> Hi Bill
>
> This has to be looked at in perspective. Everything to do with Guide is
> running fine (well, more or less; the other problems are not relevant
> here). What happens is that I start by driving the LX200 to a standard
> star at reasonable elevation - eg., Beletegeuse. Take an image,
> physically drive the scope until the image is centred, centre on the
> scope (sync) for the LX200, and then sync Guide (right-click, add star).
>
> On repositioning the scope (nearby), it is invariably off by a few
> minutes of arc (maybe 1 - 4), and remains so. I use other standard
> stars during the session, but find that centreing is always off by a few
> minutes. The importance to me is for astrometry. I try to keep all
> three successive images of the same asteroid field the same for
> blinking.
>
> > You mention that you don't get good results with the synch operation:
> >do things get worse? Better? Exactly the same? Still bad, but in
> >a different direction?
>
> I haven't noted that point. Perhaps I should do more meaningful
> measurements. Errors seem to be similar.
>
> Overall, I am fairly convinced that *I* am not following the procedure
> correctly, but because I think I am, I assume that I need to find a
> better procedure.
>
> Tests suggest to me that even after doing a local sync, the scope is
> always off by a few minutes on the next goto. I have also tried syncing
> the LX200 and then syncing Guide. Always the same result though.
>
> > One possible source of trouble is in the epoch used by LX-200 scopes.
> >I've been unable to find information about this, and it hasn't mattered
> >much in the past; we've been close enough to J2000 that the difference
> >would be less than the usual pointing error in the scopes. Guide assumes
> >that the RA/dec sent to or received from the scope ought to be in the
> >epoch of date. If I'm wrong, then you should hit Alt-J and enter
> >
> >SCOPE_EPOCH=2000
> >
> > This will adjust the coordinates sent to the scope by up to a few
> >arcminutes. I'd be _very_ interested to hear from anyone who tries this
> >out. The above capability was originally added mostly for folks with
> >home-brew LX-200 clones who needed an adjustable epoch... but it could
> >be that my assumptions about the epoch used in LX-200s have been wrong!
>
> I expect more clear skies tonight so I shall try this bit - though I
> don't believe that the LX200 is using an old epoch.
>
> best wishes
>
> Lawrence