In a message dated 7/1/2007 6:56:06 PM Central Daylight Time,
kattnerk@... writes:

My main question is: where in this process should I sync? I need to
do a sync to let the mount know which end is up. And further to the
point, can I sync with the SKY or do I need to use the key pad? If I
consult the user manual for the keypad it has a section beginning on
page 67 that describes how to use the mount with the SKY. It says in
step 5, "This procedure is only necessary if your telescope is not
pointing to the position indicated by the white crosshair circle when
you establish your link. By syncing, you will tell the SKY where
your telescope is pointing."

The mount always knows where it is, even after you have turned off the power
and re-started it at a later date. It knows this because it stores each of the
axis angles at power down. These angles are automatically calculated to be RA
and DEc numbers the moment that you send accurate time, location and date to
the mount (via keypad or via an external source - either one). Therefore, you
never need to Sync if you do not move the axes by hand via the clutches. The
mount also knows which side the scope is on (unless you move the scope by hand
with the clutches loose).

The reason you would use Sync is for setting up the mount for the first time,
or after your scope/mount has been disassembled after the last session and
moved to another location. Sync then not only tells the mount where your scope
is pointing in the sky, but also configures your mount/scope for the scope to
be on the proper side of the mounting for all subsequent objects (unless you
have placed the scope past the meridian, in which case all other objects will be
accessed past the meridian and underneath the mount).

In the keypad, we use Rcal to modify or center an object that we have just
slewed to. You need this because sometimes you cannot get a perfect go-to and
you need to center an object. This simply updates the RA/Dec position of the
servo to that of the object in the data library. Since popular planetarium
programs do not have anything other than Sync in their software (which is fine for
fork mounted SCTs because they do not have the past-the-meridian-problem), you
will then have no choice but to use this function if you want to center an
object and update its position.

With Sync, you run the risc of going slightly past the meridian to center an
object, which then re-defines the mount/scope configuration for all subsequent
slews with the scope going underneath the mount. So, unless the planetarium
software people update this and add an Rcal function to their programs, it will
remain risky to use this willy-nilly. Rcal of course will not redefine the
mount/scope, so that you can use this function with the scope well past the
meridian (for example after you have imaged for 1-2 hours and allowed the object
to track past the meridian).

Rcal in the keypad can ONLY be used after you have slewed to an object in the
KEYPAD, not after you have slewed to an object with external software because
the keypad has no way of knowing that you have slewed to Sharpless 1234567
(this type of identifying data is never sent to the mount from your external 3rd
party software, so there is no way of knowing this either in the servo or in
the keypad). It only knows that you previously slewed to M1 with the keypad.
Do not mix up Sync and Rcal features between keypad and external software, or
you will quickly find out what it means for the mount to be lost - you have
steered it into the ditch!

Rolando


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