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The Dec setting circle has been factory set to read the correct Declination of sky objects, but this setting should be
re-checked the first time the setting circles are used. With the telescope polar aligned, point the telescope as
shown in Fig. 8 and center the North Star, Polaris (Fig. 9), in the telescopic field. Polaris has a Declination of 89.2° .
With Polaris centered in the field of view, both Dec setting circles should therefore read 89.2° , using the small
indicator arrow (5, Fig. 7) located immediately under each Declination circle. The Dec setting circles can be moved
by slightly unthreading their cover plates, adjusting the circle positions, and then retightening the cover plates.
Since celestial objects move in Right Ascension, the R.A. setting circle must be set as each object is located during
an observing session. This point is explained in more detail below.
Note that the R.A. circle has two rows of numbers from 0 to 23, corresponding to the hours of a 24-hour clock. The
upper row of numbers should be used by observers in the Earth's northern hemisphere, the lower row by observers
in the Earth's southern hemisphere.
The indicator arrow (6, Fig. 7) for the R.A. setting circle is located on the opposite side of the drive base from the
position where the two fixed table tripod legs attach and immediately under the R.A. circle.
To use the setting circles, the ETX must first be polar aligned; it is advisable that the motor drive be turned on and
that a lowpower eyepiece (e.g., the SP 26mm eyepiece) be employed. Then follow this procedure:
1. Identify the celestial coordinates (R.A. and Dec) of a bright, easy-to-find
object, such as a bright star. (Avoid using Polaris or any object near
Polaris.) Coordinates of some bright stars are listed further on in this
manual, or use a sky catalog. Center this object in the telescope's field
of view.
2. Manually turn the R.A. circle (Fig. 10) to read the R.A. of the object.
3. The R.A. circle is now calibrated to read the correct R.A. of any object at
which the telescope is pointed. The Dec circle is already calibrated as
described above.
4. Without touching the setting circles, move the telescope (manually, by
unlocking the R.A. and Dec Locks, or by using the R.A. and Dec Slow-
Motion Controls) so that the setting circle indicators (5 and 6, Fig. 7)
read the R.A. and Dec coordinates of a second object that you wish to
locate.
5. If the above procedure has been followed carefully, the second object
will now be in the telescope's field of view.
Note: Since the second object (i.e., the object to be located) is in constant motion, once the R.A. circle is calibrated
(step 2, above), the telescope should be moved rapidly to read the coordinates of the second object. Otherwise the
second object will no longer be in the position indicated by the R.A. circle.
Using setting circles requires a developed technique. When using the circles for the first time, try hopping from one
bright star (the calibration star) to another bright star of known coordinates. Practice moving the telescope from one
easy-to-find object to another easy-to-find object. In this way the precision required for accurate object location will
become evident.
g. Photography Through the ETX Astro Telescope
Photography through the ETX Astro Telescope requires the addition of the optional #64 T-Adapter (see OPTIONAL
ACCESSORIES, page 14). With the #64 T-Adapter attached to the telescope (Fig. 11), through-the-telescope
photography is possible with any 35mm camera body with removable lens. In this way the telescope effectively
becomes the lens of the camera.
For through-the-telescope photography, turn the Flip-Mirror Control, (5, Fig. 11) to the "down" position, allowing
light to pass straight through the telescope and out the Photo Port (6, Fig. 1). With the Flip-Mirror Control in the
"down" position and the Photo Port's dust cover removed, the front lens of the telescope can be seen when looking
Fig. 10: Manually turning the R.A. setting
circle to read the Right Ascension of an
object.
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