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Paramount ME's
Home Position
Why bother placing a label on
the Paramount's home position? Read on!
By accurately labeling the
altitude/azimuth (Earth based) coordinates of the Paramount's home position (or
MKS-3000/MKS-4000 based telescope mount) on TheSky
display, and this is important, "AFTER" an initial accurate
star SYNC has been performed (not before) and also important "WITHOUT a
TPoint model present, you now have a visual
record of where the telescope cross hairs should be after homing. The
new cross hair position after a star sync
factors in the hour angle and declination offsets caused by an imperfect
mount with an imperfect OTA in an imperfect world. You do not want TPoint present because it
will
offset the sync position based on the TPoint model. Technically, if
TPoint is present this
new TPoint corrected position is not the accurate sync position after the
star sync and is also
subject to change.
After homing the Paramount
ME (or other mount using the
MKS control system)
if for any reason the telescope cross hairs are not falling very near or on the home position
labeled on TheSky display you immediately know there is a problem. This is simply a great
reality check and highly recommended especially for remote telescope users. Believe me
I am speaking from experience here.
Scenario - an example
This method had saved a trip to Las Campanas, Chile as a matter of fact. Ok I fess up. I had at one point synced
the Paramount GT-1100S on the WRONG side of the meridian forgetting I was
imaging in the Southern hemisphere. Note this is an issue
in the Southern Hemisphere only.
You must sync the
GT-1100S or
Paramount
ME using a star on the opposite side of the meridian as the home position. Easy to forget when you are
in Colorado and the Paramount is in Chile.
Remote Chile Site featured here <--- Click here for details, used
nearly every clear night!
Please carefully read the
latest Paramount ME User's
Guide for details about mount synchronization in the northern and
southern hemisphere.
Note the default "Hour Angle" and
Declination shown here
Homing message indicating default hour angle
and declination
Before the Paramount ME has
been accurately "synced" on a star the default home sensor position is as
follows Hour Angle = 2.00 and
Declination = 0.00. The GT-1100S values
are shown above. When these
values are the default settings you know the Paramount has not been synced
properly yet. Note
this is Hour Angle = 2.00 not Right Ascension = 2.00.
Definitions of both Right Ascension and or Hour
Angle are here.
NOTE: When you click on
the telescope cross hairs cursor position position BOTH the Right Ascension
(RA) and the Hour Angle (HA) are reported on the object information dialog.
See below and note the difference.
Right Ascension versus
Hour Angle
Note the difference between
Hour angle and
Right Ascension
The Hour Angle of the home position is ~2.00
for the default Versa-Plate position
Ok I want to clear the Sync values to
their default settings - Hour Angle = 2.00 and
Declination = 0.00 how is that done?
Inadvertently syncing on the
wrong star or syncing on the wrong side of the meridian in the southern hemisphere, are
two examples. Another example, you have the wrong date/time including the
wrong daylight option or the wrong location set in TheSky. This is
why having a label indicating the home position is a good idea. It is a
great reality check!
Also keep in mind that the
telescope left tracking will eventually cause the telescope cross hairs to
fall off the Home Label Alt/Az position over time.<---Read
about it here.
Well although this may be
confusing the following MUST BE CLEAR! Ostensibly there are 3 positions for
the home position. Why?
Home Position and telescope
cross hairs offset
Labeling all possibilities after homing
NOTE: offsets slightly exaggerated to make the point!
NOTE: There are three Possible
Cross Hair Positions after homing -
What???
1) The Home Position using
the default values of Hour Angle = 2.00 and
Declination = 0.00.
2) The Cross Hair Position
after factoring in the first accurate Star Sync
3) The Cross Hair Position after
the first Star Sync and with a TPoint model present
Which position is correct?
The above list is in order of technical accuracy. Meaning that the final
corrected label
shown after a star sync and with a good TPoint model is present is the best
and most accurate set of coordinates for the telescope cross hairs after
homing. The TPoint corrected offset position is not absolute like the default
home position, it is subject to change and is completely system dependent!
No two systems are identical therefore you have to sync and subsequently map
out the additional errors in the system using TPoint to achieve good sub
arcminute RMS pointing.
NOTE!
THE TPoint offset factored in IS
NOT THE DEFAULT HOME POSITION, the offset from the default home
position has now been properly adjusted by both the TPoint
model present based on the system and the initial Star Sync. This must be crystal clear!
You can very easily add a
label at the precise HOME position which is an Altitude/Azimuth Earth Based
marker which will not change. Use Data | User Defined-Data by choosing "Snap
To Cursor position", select "Object Type: Labels", and make sure you have
picked "Horizon Coordinates". See below.
User Defined-Data
Altitude Azimuth Label showing Home position
The object type can be the
default "Reference Point" or whatever you like
including your own custom object type
if you like. Make sure the object type is set to visible as shown below.
View | Display Explorer and just type in Reference Point next to Go to: and
you are taken directly there.
WARNING! Before adding the Alt/Az home label disable tracking so
the mount does not move from this position. If tracking is on and you take a
few minutes to add the label the position will no longer be accurate.
Telescope | Options and disable tracking by removing the check mark next to
tracking.
TIP: Now ZOOM WAY OUT
in TheSky or the cross hairs will be hard to target. The further out you are
the easier the labeling will be.
NOTE: The
Altitude/Azimuth position of the cross hair position after an initial Star
Sync will not be the same
for everyone. Even though the HOME position is an absolute position. It is important to understand this. The
offset from the default home position is completely mount/telescope
specific. Do not expect the hour angle and declination to be the default
values AFTER you have synced accurately on a star to match the defaults
settings. Simply put they will differ slightly. The smaller the discrepancy
after the sync the better the system is built overall.
Zoom in very close on telescope cross hair
after the home
Press CONTROL+Left Mouse Click
precisely on the Home position
After homing the Paramount ME
zoom all the way in on TheSky display so you can accurately mark the ALT/AZ
center of the telescope cross hair at the home position.
DO NOT move
the Paramount off of the home position and disable tracking first! Then Press CONTROL+Left Mouse click
on the EXACT center of the telescope cross hair position after the home AND
after you have Synced the telescope on a star first so the label position
reflects the adjusted offsets introduced by the errors that are specific to
your mount and OTA and other equipment.
After you have
homed the mount AND after you have performed an initial Star Sync (checking
the hour angle and declination values) IMMEDIATELY make a backup copy of the
firmware settings! This will allow you to recover from a bad sync at
anytime! I cannot stress this enough.
NOTE:
After a good initial star Sync simply make a backup copy of the
control system parameters which will have the proper Sync offsets.
GREAT IDEA!! This can save you a trip back to
your scope if your
system is many miles away or a continent away. Painless, quite simple to do,
and ALWAYS worth saving AFTER every proper Sync just in case.
By using the option "SAVE" on
the More Settings Dialog the firmware parameters can be saved to a file on
your hard disk. This way you can ALWAYS get back to an accurate sync. That
is regardless of an incorrect Sync. Just use the option to load the file you
have saved with the proper Sync values.
When asked for a label enter
"Home Position" or something to that affect. Note the altitude azimuth
position of the center of the screen or the cursor position can also be
added to the status bar for reference if you like. Next add the homing position
label to TheSky document. Use whatever you like for a title here.
Now add the Alt/Az label
Save TheSky document
(File Save As)
IMPORTANT! Save your document file in
TheSky AFTER adding the label on the home position. Use File | Save As and give the
document a good name like HOME.SKY. You may even want to make the
document R/O (Read Only using Windows Explorer) so you don't accidentally
wipe out this important label position.
View | Display Explorer
Enable type Reference Point
If the object type is not
visible you won't see the label. To change the size of the font or
font color use the Display Properties of Reference Point. Sometimes increasing the
font size or changing its' color will help to make the label easier to see
in TheSky.
Ok you have your home position
accurately labeled on TheSky display but find that the telescope cross hairs
are no where near the label for the Home Position. Now what??? Houston we have a problem!
First make sure TheSky is set
to use the PC clock (an error message will show if this is not the case),
and check that the location settings and Date/Time and Daylight option are
all correct in TheSky. AND lastly check the PC's time. If you are 100% sure
that all of the above are correct and homing will not place the telescope
cross hair on the label the most likely cause is a bad "Sync" meaning the
telescope is inadvertently synced on the wrong star. Don't Panic!
Here is a simple reality
check.
The following shows what is considered a normal or reasonable pair of
Sync values for the home sensor position on the Telescope | Options | More
Settings dialog. Not exactly HA: 2.00 and Dec: 0.00
but very close. ASSUMING your versa-plate has been mounted in
the default position on the DEC axis and assuming the telescope has been
mounted reasonably square with the plate the values will be very close.
If you find that you are
several degrees in error after more than one attempt to accurately sync on a
star your versa-plate is either not in the default position or the mounting of
the OTA on the Paramount is not optimal, i.e. not very orthogonal or
perpendicular. As in if you have a 1 degree error or more in your OTA
mounting your Sync value will reflect that error! Again, checking here is a
great reality check!
Telescope | Options | More
Settings
Looks good to me!
NOTE: If the
values for the Home Sensor Position shown above are HA: 2.00 and
Dec:0.00 the defaults this indicates you have not Synced the mount on a
star yet. Again, the chances are one in a million that your sync values will
match the perfect default settings. In any case ALWAYS re-sync on a star
then check these values again to be sure or when you see the defaults.
After loading the firmware
backup file that contains your
proper Sync values if
TPoint is present you will then have to
Sync back into the TPoint Model.
Confused???
The reason being is the offset
that TPoint introduces
in addition to the hardware offsets (that are saved in the backup) is not
factored in yet. So by Syncing
back into the model after loading your proper initial star sync you are
now right back where you were, but not before.
Load firmware backup first
center object then Sync back into the model
Now you are back to square one
and ready to go.
A bad sync is obvious when you
have chosen to label the
accurate home position on TheSky display. After homing, the telescope
cross hairs are no where near the homing label and the Sync values in the
More Settings dialog are no
longer valid. See below.
This can't be right!
Can it?
Actually it could be but your
OTA would have to be mounted many many degrees in error on the DEC axis or
the Versa-Plate was not mounted in the proper position. Again, after an
initial star Sync even with this error assuming it exists the
labeling of the home position
still works!!! That is because the offsets are taken care of by the
Sync. The newly labeled home position will be exactly this far off from the
defaults so the telescope cross hairs will still fall on the home position.
Now you see why I say add the homing label AFTER an initial
star sync!
There are times when you find
you want to put the Paramount/control system back to its' original state. This allows you to
start from a clean slate.
Setting the default control
system parameters
Choose Defaults then select mount
Next immediately after
performing an accurate first time star Sync - Save the firmware settings to
disk as a back-up!
Assuming you previously had an
accurate sync and a good working TPoint model if you find pointing errors
caused by incorrect time or pointing errors introduced by changing OTA's or
imaging cameras you can use the option to Sync back into the model.
See below. This dialog appears when you attempt to re-Sync with a TPoint
model present.
Equipment change
or error in time
It is always a good to idea to
try this first BEFORE starting off on another full mapping run. Ignore the
least accurate warning and more often than not this can put you back to
where you were. At least very close. If not or you are still not happy with
the pointing go back and start over building a whole new TPoint model.
Displaying Alt/Az on the
status bar
You can also add the option to
display the center of the screen in Altitude Azimuth coordinates on the
Status Bar. View | Status Bar and check mark the option. Note
the Alt/Az position now on the lower right of TheSky display.
Status Bar Center on cross hair
Screen centered at Home Position
Don't Panic. This is perfectly
normal when TPoint is present. Why? Because it is TPoint's job to alter the
telescope's coordinates based on the model. To see this is in fact the case
here is an easy test. Just disable the TPoint corrections and note the
change in the cross hairs position. The TPoint correction can be an offset
many arcseconds to even arcminutes!
Disabling TPoint,
temporarily
Remove the check mark
Warning! Don't
forget to enable it when done!
Again speaking from experience
here, DON'T forget to enable TPoint when done! Many years ago
at the Riverside Telescope Makers Conference to demonstrate how well TPoint
works I turned it off. All objects slewed to were somewhere on the chip but
some objects fell many arcminutes off center. Frustrated I finally realized
that TPoint was simply turned off. After enabling TPoint I made a script
that slewed to a dozen Messier objects currently above the horizon. When the
images were all taken I did a Blink Compare in CCDSoft. To my pleasant
surprise no object fell off center more then about 30 arcseconds. Whew!
Secondly
If the telescope is currently
tracking, in time the telescope will fall off the Home Label Alt/Az position.
This too is perfectly normal behavior.
Disable tracking when performing the test so the
telescope does NOT drift off the home (Alt/Az) position.
Telescope tracking after
10 minutes
15 arcseconds/second - sidereal rate
To demonstrate. Note the
angular separation between the home label on the left and the current
telescope position in only 10 minutes time - 2d 32m 55 seconds. The drift in
RA is the telescope tracking at the sidereal rate or ~1 degree every 4
minutes 15arcseconds/second. By disabling the telescope tracking prior to
homing the telescope cross hairs will not move off the home position.
Keep in mind the above is also
a great way to see if TPoint is working properly. If TPoint make pointing
worse when enabled there is a problem with the data or possibly the terms
applied and or both!
NOTE:
TheSky's
on-line documentation has additional detailed information!
The local sidereal time (LST) is equal to the
current
right ascension of the
local meridian. One sidereal day is equal to the amount of time
required for the Earth's rotation to turn it through all 24 hours of
right ascension (approximately 23 hours, 56 minutes of calendar time).
The "Hour
Angle" for any given object
is the difference between the the
Local Sidereal
Time (LST) and the Right Ascension
of the object in question.
The component of an object's celestial coordinates that indicates its
position in the east-west direction; expressed in hours, minutes and
seconds.
Note when a star or other objects is on the meridian (in transit) the
Right Ascension of the star is equal
to the local
sidereal time (LST). You can clearly see this using TheSky by enabling
the Local Sidereal Time on the Status bar and then clicking on any star that
is currently on the meridian (in transit).
Declination is the component
of an object's celestial coordinates that indicates its position in the
north-south direction and is expressed in degrees, minutes and seconds.
Also note that a "Google
Search" on any of these topics will also yield many other sources with good
information. Many of these links will also show exactly how these values
computed.
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