Precise Polar Alignment - Meade LX90 Instruction Manual

Begin polar aligning the telescope by locating Polaris. Finding Polaris is simple. Most people
recognize the "Big Dipper." The Big Dipper has two stars that point the way to Polaris (Fig. 29).
Once Polaris is found, it is a straightforward procedure to obtain a rough polar alignment.
To line up with Polaris, follow the procedure described below. Refer to the instruction sheet
included with your equatorial wedge for information about attaching the wedge to the telescope
and also about using the azimuth and latitude controls.
1.
2.
Tip:
You can check if the
Declination is set at true
90° in step 2c. Look
through the eyepiece and
rapidly slew the optical
tube on the R.A. axis. If all
the stars rotate around the
center of the field of view,
the Declination is set at
90°. If the stars arc out of
the field of view, slew the
optical tube on the
Declination axis until you
achieve the centering
effect.
At this point, your polar alignment is good enough for casual observations. There are times,
however, when you will need to have precise polar alignment, such as when making fine
astrophotographs.
Once the latitude angle of the wedge has been fixed and locked-in according to the above
procedure, it is not necessary to repeat this operation each time the telescope is used, unless
you move a considerable distance North or South from your original observing position.
(Approximately 70 miles movement in North-South observing position is equivalent to 1° in
latitude change.) The wedge may be detached from the field tripod and, as long as the latitude
angle setting is not altered and the field tripod is leveled, it will retain the correct latitude setting
when replaced on the tripod.
The first time you polar align the telescope, check the calibration of the Declination setting
circle (11, Fig. 1). After performing the polar alignment procedure, center the star Polaris in the
telescope field. Remove the knurled central hub of the Declination setting circle and move the
setting circle so that the molded triangular pointer to 90°.

Precise Polar Alignment

It should be emphasized that while doing casual observing, precise alignment of the telescope's
polar axis to the celestial pole is not necessary. Don't allow a time-consuming effort at lining up
with the pole to interfere with your basic enjoyment of the telescope. For long-exposure
photography, however, the ground rules are quite different, and precise polar alignment is not
only advisable, but almost essential.
Even though the
rections required during the course of a long-exposure photograph, the better. ("Long-exposure"
means any photograph of a celestial object that last for 10 minutes or longer). In particular, the
number of Declination corrections required is a direct function of the precision of polar
alignment.
Precise polar alignment requires the use of a crosshair eyepiece. The Meade Illuminated
Reticle Eyepiece (see "OPTIONAL ACCESSORIES
but it is also preferable to increase the effective magnification through the use of a 2X or 3X
Barlow lens as well. Follow this procedure (particularly if the pole star is not visible), sometimes
better known as the "Drift" method:
Select "Setup: Telescope" from the AutoStar menus. Press ENTER. Scroll to "Telescope:
Mount" and press ENTER. Scroll to "Scope Mounting: Polar" and press ENTER. The tele-
scope mount is now set to the polar mode.
Press MODE until "Select Item: Setup" displays. Press ENTER. "Setup: Align" displays.
Press ENTER. Scroll to "Align: One-Star" and press ENTER. AutoStar now prompts you
to set the telescope in the polar home position.
a. Using the bubble level of the wedge, adjust the tripod legs so that the bubble is level.
b. Set the wedge to your observing latitude.
c. Using the Up and Down Arrow keys, rotate the telescope tube in Declination so that
the telescope's Declination reads 90°, that is the molded Dec pointer (11, Fig. 1) is
pointed to 90° on the Dec. setting circle.
d. Loosen the R.A. lock, and rotate the fork arms to the 00 position H. A. on the R.A.
setting circle.
e. Press ENTER. The telescope slews to Polaris.
f. Use the azimuth and latitude controls on the wedge to center Polaris in the field of
view. Do not use the AutoStar handbox during this process. When Polaris is centered,
press ENTER. The telescope is now polar aligned.
telescopes offers a sophisticated drive system, the fewer tracking cor-
LX90
, page 41) is well-suited in this application,
"
50