Polar Alignment of LX200R and Ultra Wedge
For
The Southern Hemisphere by Chris James
Overview
This document goes thru the
process required to Polar Align the LX200R using a Ultra Wedge in the Southern
Hemisphere. It differs from that described in the manual for the Northern
Hemisphere in that it takes measures to more accurately place the scope in the
Polar Position as the star used by auto star for alignment Sigma Octanis cannot
be seen with the naked eye under most circumstances, which is not the case for
Polaris used in the northern hemisphere. As a result it uses methods to place
the scope in the Polar position that are normally used during the day. This
places the alignment star in the view scope at the end of this procedure to
allow the normal process to be used to complete the polar alignment procedure.
You will need a Compass,
Spirit Level and a Protractor to complete this process.
Setup Tripod
a) Orientate the
tripod using a compass so that tangent arm on the tripod is pointing north.
Dont forget to compensate for magnetic north in the area.
b) Using a spirit
level, adjust the length of the three legs of the tripod to achieve level in
all directions on the head of the tripod.
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Level Tripod Head |
Orientate Tripod Using A Compass |
Mount the wedge on
the tripod using the Manual Knob/Compass and the three Button Head bolts. Make the
button head bolts firm but not tight to allow the wedge to rotate on the head
of the tripod to perform adjustments.
Confirm the wedge
is still aligned in the North/South direction with the compass mounted in the
Manual Knob. You can correct any alignment with the Azimuth Control Knob on the
wedge or by moving the tripod legs, depending on amount of the error you need
to compensate for. Note: the wedge will now be orientated in such a manner so
that when the scope is place on it, the control box of the scope will be facing
south.
Using the bubble
level in Ultra Wedge, confirm the wedge is still level in all directions.
Adjust tripod legs if required to achieve level. If you have not already done so,
confirm the bubble in the Ultra Wedge is reading true by using an alternative
external spirit level before you solely depend on the inbuilt bubble level.
Adjust the Tilt
Plate for your latitude. The latitude scale on the side of the wedge should be
used as a guide only. Once you are close, use a protractor and the
complementary angle for your latitude. Complementary Angle = 90 minus your
Latitude. For latitude of 32 degrees, the complementary angle is, 90 minus 32 =
58 degrees. Placing the protractor on the tilt plate adjust the fine latitude
control knob until the protractor reads the complementary angle of 58 degrees.
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Setting Tilt Plate Complementary Angle |
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Before attempting
to sit the scope base on the tilt panel, insert the single long bolt and washer
into the scope base using the hole at the opposite end to the auto star
interface panel. Use just enough thread to ensure it can hold the scope on its
own but not too much to allow you to slip it through the mounting slot on the
tilt plane. To make this easier, you can lay the bolt in the tilt panel slot
and mark the depth of the tilt panel on the bolt using a pen, before inserting
it into the scope base.
Release the RA
clutch and turn the forks so that one arm of the fork is opposite the interface
panel, then lock the RA clutch again.
You can now lift
the scope onto the tilt plane sliding the one bolt on the telescope base
through the mounting slot on the tilt plane of the wedge.
Align the
telescope base so that all three remaining holes in the telescope base and the
tilt plane align.
Now use the T-Bar
to take some of the weight for safety reasons, dont tighten it too much yet
until you have insert and started the thread on the remaining two bolts through
the tilt plane to the scope base.
Now tighten all
four bolts and ensure the scope base is flush with the tilt panel.
The proceeding
section will assume that the view scope has been mounted and calibrated so mount
all hardware including, focusing unit, diagonal prism, 9mm Illuminated Reticle
eyepiece and view scope.
Release the RA
clutch and place the place the fork arms in the middle of its RA movement.
Checking its travel between the RA stops should show it has about two turns
between stops, so lock the RA clutch about one turn from one of these stops.
Set Polar Home Position
At this stage auto star has
been turned on and the following has been completed:
Smart drive init
has completed.
GPS fix has completed.
Polar mount has
been selected in the telescope setup menu.
You have selected
Align scope and chosen the Easy Polar Alignment option.
Auto Star is now
prompting you to place the scope in the Polar Home Position.
Adjusting the RA Zero Position
As you have
centered the RA movement before hand, use the Auto Star controller to rotate
the fork arms to the 00 position so that the center tick on the arms and base
align.
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Setting RA To Zero |
Place the sprit level
across the fork arms and fine tune the RA position so that the spirit level
reads true, you can reduce the RA speed to make this adjustment real easy when
using the sprit level.
Alternatively you
can point the telescope vertically up and place the spirit level across the
telescope cover and fine tune the RA position so that the spirit level reads
true.
Adjusting the DEC 90 degree Position
Release the Dec
clutch and rotate the OTA so the DEC dial reads 90 degrees. Now place the
protractor on the OTA and fine tune the Dec position with the Auto Star
controls using a slow speed, so that the protractor reads your latitude in
degrees, 32 degrees for example.
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Adjust Dec To Your Latitude |
Now quickly recheck the following:
1) Is the Bubble
on the Wedge still true?
2) Is the RA
indicator roughly on the tick marks at the base and fork arms and the spirit
level across the fork arms showing level?
3) Is the Dec
indicator showing approx 90 Degrees and the protractor indicating your latitude
when placed along the OAT?
4) Is the scope
pointing at the point in the sky where you imagine the South Celestial Pole to
be?
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Polar Position Facing SCP |
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Press ENTER to AutoStar
If you where able
to answer yes to all of the above, then we are now ready to proceed by pressing
ENTER to allow AutoStar to continue now that you have placed the scope in the
Polar Home Position.
If its not dark
enough yet to see Sigma Octanis in your view scope, you may consider using this
time while you wait, to Train your drives (RA & DEC) on a distant
terrestrial object and then come back to this point. Training the drives is not
covered in this document.
AutoStar now slews to the Star Sigma Octanis
AutoStar now slews
to Sigma Octanis, dont be surprised if what seems a
small movement in the sky may result in a relatively long slew in RA for the
scope to arrive at Sigma Octanis. The length of the
RA slew will depend on the Local Sidereal Time and date you are doing this alignment.
In other words Sigma Octanis is quite close to the South Celestial Pole but the
scope may take a while to slew to it depending on the date and time.
A word of caution, this possible long RA slew
may leave the scope in such a position that you cannot reach the viewfinder /
eyepiece in some orientations. More importantly, if you are not expecting this
movement, depending on your setup, you may damage some expensive accessories
that you may have attached to the scope, such as SLR cameras, as it attempts to
slew through positions these attachments cant go. Dont
get a nasty surprise in the dark, know your setup limitations, if any in
advance!
Sigma Octanis, is quite dim and under most conditions you will
need binoculars or the view scope to see it. I have exaggerated its size in the
chart below. Check Sigma Octanis location on your sky map to ensure you are
happy where it should appear in the sky. RA = 21h 15.515m DEC = 88 deg 55.663m
To find it in the sky, start at the Southern Cross, trace out four times the length of the cross heading towards the SCP. Using the binoculars look in that area and pan around to find three faint stars that form an isosceles triangle that fit within the field of view of the binoculars. Now the two stars that form the side of the triangle that are 90 degrees to the line that you have just drawn from the Southern Cross are Chi Octantis and Sigma Octantis, the third star of the triangle is Tau Octantis.
Once AutoStar has
completed its slew to the Star Sigma Octanis,
With the assistance of the view scope, centre Sigma Octanis in the 9mm Illuminated Reticle eyepiece using the Wedges Azimuth and Latitude controls, do not use the arrow keys on AutoStar. The view scope will display all three stars (Chi, Sigma & Tau Octanis) whilst the field of view of the eyepiece will only display the one. If you have taken care with the setup to this point, Sigma Octanis should be in your eyepiece. If its not, try moving the Azimuth control on the wedge first to find it as its more likely you have made an error aligning North/South with your compass then the Latitude on the tilt plate with the protractor
When you have
Sigma Octanis in the center of the eye piece press ENTER on AutoStar.
AutoStar will now
select a star from its database and slew to it. Once it has completed slewing,
use the arrow keys on AutoStar to center the selected star in the eyepiece then
press ENTER.
AutoStar will now
select a second star from its database and slew to it. Once it has completed
slewing, use the arrow keys on AutoStar to center the selected star in the
eyepiece then press ENTER.
This should
complete the rough Polar alignment of the wedge and the alignment of AutoStar
to to-nights sky.
Drift Polar Alignment ( Precise Polar Alignment )
If you have done
the proceeding Polar Alignment correctly, this section should only be a fine
tune of the polar alignment required for astrophotography.
If you where
unable to complete the proceeding Polar Alignment because for example Sigma
Octanis was not visible, then the Polar Alignment can still be completed using
the drift method. It just means your starting point may be more off alignment
and this step may take a little longer then would otherwise be the case.
Fine
Adjustment of Wedges Azimuth
Place the 9mm
Illuminated Reticle Eyepiece into the eyepiece holder of the telescope. With
the telescope now tracking, slew the telescope to a bright star near the
meridian close to zenith. Youll find that nearing
straight up brings the Dec close to your latitude in degrees.
Using the arrow
keys on the remote key pad of autostar, move the scope back and forth in RA.
Adjust the cross line pattern to align the star movement to the RA plane.
Ignoring any RA
drift, compensate for any North/South drift by adjusting the wedges Azimuth
Control Knob. Keep doing this until no noticeable drift occurring over 15
minutes.
In Short:
1.
If the start drifts south in the eyepiece adjust the
Azimuth knob to move the start east in the eyepiece then re-centre it by using
the autostar controls.
2.
If the star drifts north, adjust the Azimuth knob on
the polar mount to move the start west in the eyepiece then re-centre it by
using the auto star controls.
Fine
Adjustment of Wedges Latitude
Slew the telescope
to a bright star near the Eastern or Western Horizon but still near the
celestial equator.
Ignoring any RA
drift, compensate for North/South drift by adjusting the wedges Latitude
Control Knob. Keep doing this until no noticeable drift occurs over 15 minutes.
In Short:
- Use the Tilt Knob on the Polar Mount to move
the star in the eyepiece in the opposite direction to the North/South
drift.
Keep repeating the Azimuth and Latitude adjustments above until the
changes in one have little effect on the other.
Once you are confident with this process, you may consider a short cut
process that makes better use of the setup time for a astro imaging session.
The url of the short cut process can be found @
http://www.cwjames.info/astro/howto/polaralignment_short_cut.htm
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Written by: Chris James |
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http://www.cwjames.info/astro/ |