Re: Sync vs Recaculate

Roland Christen

In a message dated 4/10/2008 4:05:19 PM Central Daylight Time,
llp41astro@... writes:

Howard or Roland,
I will repeat Dean Salman's question of yesterday as there has been no
response. What is the relationship of the Sync in Maxim compared to
AP's Sync versus Recalibrate? Is it safe to use?
Sync redefines the relationship between telescope and mount. Recal simply
updates present position and does not redefine the relationship of scope and

The relationship of scope to mount is normally defined the first time you put
mount and scope together. If you point the scope to a star to the east of the
meridian with the scope placed on the west side of the mount, you have
defined the relationship of scope to mount as being thus: scope always on the top
side of the mount (p.s vice versa works also). However, since this is a German
Equatorial, you can also define the scope to be underneath the mount. The way
you would do this is to place the scope on the east side of the mount, acquire
a star on the east side of the meridian line and do a "Sync". The mount will
now aquire all objects with the scope underneath the mount. If you have a short
enough scope and it clears the pier in all positions, this is not a problem.
However, in 99.99% of the cases, the scope will probably hit the pier, so this
relationship should be avoided.

Therefore, if your external program does not know what side of the meridian
your telescope happens to be in when it issues a "Sync" command, it could very
well redefine the relationship for the scope to be on the wrong side, and all
subsequent slews will attempt to pick up the object with the scope underneath
the mount. For this reason we have a "Recal" command (have had it since day
one!) on our mounts so that a program (any program) can use this command to
update the present position without redefining the scope/mount relationship.

Why don't all programs use this command? Reason is that the "Sync" function
was first used by Meade, and they had no need for a seperate Recal. Why?
Because in a fork mount it is not a problem. One can place the scope on any side of
the fork without the scope running into the pier. GEMs do not work this way.
They can only safely go up to the meridian and must do a meridian flip when
going to objects on the other side. Forks do not have this problem - thus no
seperate Recal is needed.

Bottom line is this: if you KNOW FOR SURE that the object you will issue a
"Sync" command is really truly on the proper side of the meridian line, then it
is ok to use Sync. If you are NOT SURE, or if you are beyond the meridian line
because you were imaging and tracking beyond the meridian, then it is not
safe to use Sync, and you need to issue a Recal. If the program does not have
Recal command, then you are out of luck.


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