Nexstar SynScan User Manual

Page 17

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Generally speaking the SynScan

TM

produces pointing and tracking accuracies adaquate for most applications.

However, if higher precision is required, for example for astro-photography, accurate polar alignment and
"cone" error calibration may be required. See the manual for

mount for information on accurate

polar alignment using the polarscope.

"Cone" error is a common inaccuracy found on all German equatorial mount. It is a result from the optical

axis not being aligned to the R.A. axis of the mount. This affects the pointing accuracy of the
Three-Star Alignment automatically compensates for the "Cone" error. If you choose One-Star or Two-Star
Alignment method, you will need to perform manual mount calibration to eliminate the "cone" error. The
following calibration procedure should be performed before the initial use of the telescope and periodically
thereafter to ensure the accuracy.

Testing for Cone Error

This test is done at night using two bright stars located on the opposite side of the sky. Make sure the
telescope is properly polar-aligned using the polarscope. Perform the One-star Alignment using an eastern
star as the alignment star (see One-star Alignment). After the star alignment, choose a bright star on the
western sky from the

object database and have the telescope slew to the star. If the optical axis

is perfectly aligned to the R.A. axis, the telescope will accurately put the star in the center of the eyepiece.
In this case, there is no "cone" error in your telescope setup and you will not need to perform the

calibration. It is acceptable if the star is slightly off-center as long as it is in the eyepeiece view and close to

the center. Many factors determine the pointing accuracy of the

for example incorrect star

alignment, R.A. or

lock knob being lose, or "cone" error. If your telescope puts the star outside the

eyepiece view, you need to first determine whether it is "cone" error that causes the pointing inaccuracy. To
find out, simply move the telescope in R.A. axis by pressing the Left or Right direction key. If the star can
be moved into the eyepiece view without adjusting the

axis, it is likely that "cone" error exists in your

telescope setup.

Calibration Procedure

1. Insert the illuminated reticle eyepiece. Make sure that the telescope is properly set up and balanced, and

the finderscope is perfectly aligned with the telescope tube.

movements

Required accessory. Illuminated

in the reticle eyepiece. If you are already familiar

reticle

Step 2 to

4

is to

R.A.

with double

with the

you

may skip to step

5.

crossline pattern. Depending

on

the

design of your mounting plate

2.

Find any bright star and place it in the center of the

(dovetail bar), modifications may

eyepiece view.

be required. (See step

10

for the

3.

Look into the eyepiece. Move the telescope in R.A.

required mechanism on the

axis using the R.A. direction keys on the hand control

mounting plate.)

while carefully observing the movement of the star.

4. Keep moving the the telescope in R.A. axis back and

forth to keep the star within the eyepiece view. Rotate

the eyepiece until the movement of the star becomes

parallel to (or matches) any set of the lines
This set of lines will represent R.A. movement in the

movement

course of this procedure, and the perpendicular lines
will represent

movement. Tigthen the set screws

to secure the eyepiece in place. Make sure that the
eyepiece will remain stationary when the telescope is
being rotated.

5. Point the telescope to North and set the latitude scale

to your local latitude using the altitude adjustment T-
bolts, or place Polaris on the crosshair of the

polarscope if your polarscope is perfectly aligned with

the rotation axis of the mount.

eyepiece view

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