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For The Southern Hemisphere by Chris James Shortcut - Process |
When and Why
To Use This Process
This shortcut process
described here, assumes that the reader is familiar with the full process
described in the polar alignment document located on this web site @ http://www.cwjames.info/astro/howto/polaralignment.htm
In order to make more
efficient use of the time taken to setup prior to an imaging session I have
separated the Drift Alignment process and Autostars Synch to the night sky for
the goto functionality.
This allows you make the best
use of the time before the sun sets by allowing you to fit all the required
accessories for the evenings imaging session during daylight whilst waiting for
the stars to come out to begin the drift alignment. Accessories such as and
guide scopes, cameras, dew shields and cameras etc can now be fitted and you
will not be required to move the scope to the Polar Home Position to complete
Auto Stars alignment. By separating Auto Stars synch process you can then Synch
Autostar to the night sky without having to move your fully equipped scope
around the SCP as would normally be the case.
Now when the stars begin to
show, you can now do your drift alignment with the scope fully equipped with
the required accessories and once the drift alignment has been completed a new
process is used to synch Auto Star for the goto function to operate correctly.
Overview Of
The Steps Required
1. Mount The Scope On Wedge. (as per the original polar
alignment document)
2. Attach All The Required Accessories To Scope.
3. Setup Autostar to begin tracking.
4. Do The Drift Alignment. (as per the original polar
alignment document)
5. Align Autostar To the Night Sky.
1 -
To mount the scope, follow
all the steps as detailed in the full polar alignment document on this web
site.
Stop following the instructions
from the full documentation when you get to the heading, Set Polar Home Position
Dont take any short cuts to
this point.
Note, if the basic
wedge alignment is NOT true at this stage, you will not be able to achieve a
good Drift Alignment or be able to Synch Autostar to the night sky so you can
use the GOTO will any degree of accuracy. So double check with your compass
(factoring in your local magnetic deviation) that the wedge is pointing is the
right direction. Use your spirit level to confirm that the base of the Wedge is
level in all directions and the Tilt Plate has been set to the complementary
angle for your latitude as described in the full document using your
protractor.
2 - Attach All The Required
Accessories To Scope
Continue attaching all the
required accessories to the scope for the evenings session, for example, Guide
scope, dew shield and heaters, wiring looms for camera and other electronics as
required. Align the guide scope, finder device to the main scopes axis and
complete any balancing of the final setup as required.
Once everything is attached
and ready ensure the RA clutch is locked in the middle of the RA travel as
described in the full document.
3 -
Setup Autostar To Begin Tracking
Now turn the power on to Auto
Star and wait for Smart drive init to complete. I will assume you have setup
the scope and placed Autostar in the Polar mode for use with the wedge at this
stage. If not go back and ensure its in Polar mode before proceeding.
Basically we need to tell
Autostar NOT to do the alignment routine by pressing the Mode key when prompted
to Align or go to the Menu, we will press mode to go to the menu. Auto star
will then take a GPS fix to get your location and the time and date so it can
workout the Local Sidereal Time. It is recommended that you set GPS Alignment
to AT START as this will help avoid one of the firmware bugs in Autostar. Once
the GPS alignment has completed, continue to press the
mode key to escape the Alignment menus until you are at the top level menu.
Autostar has now done a GPS
fix so it knows your location and the Local Sidereal Time and it is now
tracking the sky with the RA motor only running. We have NOT synch it to the
sky, so any GOTO commands will not work at this stage, however we will come
back later to fix this problem.
A summary of Auto Stars
Responses and your input is as below.
|
Autostar Responses |
Your Input |
|
Press 0 To Align or Mode for Menu |
Press Mode
(To go to the Menu) |
|
Taking a GPS Fix |
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|
Align: Easy |
Press Mode
(To escape this level of Menu) |
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Setup: Align |
Press Mode
(To escape this level of Menu) |
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Select Item |
Do nothing
- Auto Star will now be tracking |
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4 - Do The Drift Alignment
If the sky is dark enough to see
stars you can now begin to do your drift alignment. I will not explain this
procedure in detail here as it is explained in full in the full Polar Alignment
document on this web site.
Full Polar Alignment document
can be found at http://www.cwjames.info/astro/howto/polaralignment.htm
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Azimuth Adjustment |
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Latitude
Adjustment |
5 - Align Autostar To The
Night Sky
Now that the drift
alignment has been completed all that remains is to synch Autostar to the night
sky. If you remember we bypassed this section before so currently our GOTO
commands will not work. We need to slightly modify the standard polar alignment
process in order to keep the imaging train clear of anything now that we have
the all the required accessories attached to the scope. We will align Autostar
to the night sky without risking the imaging train but at the same time let
Autostar know where the hard RA stops are.
We are now going
to do a modified Polar One Star alignment.
From Autostars top
level menu select ALIGN and then select ONE STAR. Autostar will now prompt you
to put the scope in the Polar Home position. When setting the scope to the
Polar Home position ONLY do the HA location for polar home and leave the OTA in
a safe position so your imaging train clears the base. Setting the DEC to
somewhere close to 0 for example should keep the imaging train clear of the
base. The full instructions for setting HA location for the Polar Home position
are in the full polar documentation under the heading ADJUSTING THE RA ZERO
POSITION.
Once you have the
HA location set correctly, press ENTER and Autostar will now slew to Sigma
Octanis. When the slew is complete simply press the ENTER key without checking
the star in the eyepiece/CCD as we have already done a drift alignment.
Autostar will now select an alignment star and slew to it. When the slew is
complete, release the Dec clutch and move the OTA to centre the selected star.
One you have got the star approximately centered as best as possible in the
eyepiece/CCD then you can lock the Dec clutch and complete the centering with
Autostars arrow keys and then press ENTER to complete the Polar One Star
Alignment.
Autostar should now be
able to use its GOTO function to other objects in its data base.
What I strongly
recommend doing now before going to your first dim deep sky object is to select
a bright object close to your dim target. Now do a goto to the bright object
and when the slew has completed, use auto arrows keys if required to centre the
bright object on your CCD. Dont unlock the clutches this time, just use auto
stars arrow keys to centre the bright target. Now hold the ENTER key down for 3
seconds plus and release it. Autostar will be once again prompting you to press
ENTER to synch the target. Press the ENTER key when you have the target
centered on the CCD.
Now do a GOTO to
your dim target and the chances are it will be on your CCD after doing an
appropriate exposure for your dim object. Once you have the dim object centered
on your CCD, do another synch on it as just described above.
I strongly
recommend you repeat this process for every new dim target you select,
especially if its in a area of the sky some distance from your last synch target.
In other words, for every new dim target, select a bright target close by and
synch on it first using your CCD, then use the goto to go to the dim target.
Once the dim target is centered on the CCD then also synch on it. The accuracy
of your goto will get better and better as you select more targets during the
course of the evening with your targets appearing on the CCD after the slew to
it has completed on the first go. Alternatively you could turn on Autostar
built-in High Precision Mode which effectively does this for you. I like to
choose when and what bright object to use to synch on and as a result I leave
this mode turned off, you however may choose to turn it on.
Important - If you find that the goto
accuracy is only good for objects close to where you have done your last synch,
then I strongly suggest you re check the wedges basic alignment with your
compass, spirit level and protractor as described in the full Polar Alignment
document and confirm the Drift Alignment is ok. Either one of these alignments
being incorrect will directly impact on Autostars ability to do accurate goto
commands for all objects across the night sky. NO amount of target synching can make the goto work for all objects
under these conditions.
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Written by: Chris James |
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http://www.cwjames.info/astro/ |