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3. CEM25 Mount Assembly
3.1. Introduction
You have just purchased a telescope mount that is capable of taking you to a new level of
astronomy. No matter which telescope or optical tube assembly (OTA) you select to install on the mount,
the overall performance will be greatly enhanced. In order for you to get the optimum performance from the
mount and OTA combination, you must assemble and adjust the mount correctly. The following
fundamentals of telescope mounts are included to help you understand the big picture before you get into
the specific details of the CEM25 mount.
Telescope mounts are either equatorial mounts or altitude-azimuth (Alt-Az) mounts. Both types of
mounts rotate the OTA around two perpendicular axes to point to a desired object in the night sky. An
equatorial mount has the right ascension (R.A.) axis aligned with the celestial North Pole (CNP), or celestial
South Pole (CSP) in southern hemisphere, to provide rotation matching the celestial sphere rotation around
the Earth and the declination axis (DEC) to provide elevation relative to the celestial equator. Since all
celestial objects appear to rotate around the CNP, the R.A. axis allows the OTA to rotate with the celestial
sphere and provide accurate tracking for visual observations and astrophotography. R.A. is the celestial
equivalent of longitude. Like longitude, R.A. measures an angle that increases toward the East as
measured from a zero reference point on the celestial equator. An Alt-Az mount has a horizontal axis to
provide vertical (altitude) OTA movement from the local horizon and a vertical axis to provide horizontal
(azimuth) OTA movement, similar to compass headings. An Alt-Az mount can provide tracking that is good
enough for visual observing and short exposure photos, but not good enough for serious astrophotography.
Alt-Az mounts require star alignments for the OTA to track stars and they do not have adjustment
components on the mount. Equatorial mounts require alignment of the mount components as well as star
alignments for accurate OTA tracking.
In order to provide the required Polar Axis alignment, equatorial mounts use a combination of both
mount types described above. The adjustable part of the mount moves in the Alt-Az mode in order to align
the R.A. axis, also known as the mount’s Polar Axis, with the CNP. These Polar Axis adjustments do not
involve any rotations of the OTA about the R.A. or DEC axes and can be performed without the OTA
installed. The first step is to make an approximate azimuth alignment of the Polar Axis by aligning the
specified tripod leg or reference point toward True North using a compass for reference (you must allow for
the variation between True and Magnetic North at your location). Precise horizontal alignment of the Polar
Axis is accomplished with azimuth adjustments on the mount. The second step is to adjust the Polar Axis
vertically (altitude) above the North horizon by setting the observer’s latitude on the provided latitude scale.
This procedure is based on the fundamental geometry of the Earth’s coordinate system in conjunction with
the concept of the celestial sphere. You can verify this by visualizing yourself at the North Pole (latitude
N90°) and Polaris will be 90° from the horizon, or directly overhead. These steps will place the Polar Axis
very close to the CNP. Both of the above adjustments can be enhanced by the use of an opening along the
R.A. axis that allows direct viewing of the North Star and the use of a polar scope to view through this
opening. If you are going to get the most out of your equatorial mount it is essential to understand the
concept of the Polar Axis and how the equatorial mount helps you establish and maintain a true Polar Axis
alignment. Now, you are ready to perform star alignments using the equatorial mount’s electronic controller
and enjoy the night sky.
The CEM25 mount is a next-generation equatorial mount that provides the precision alignment
capabilities required for today’s complete astronomy solution. The following sections of this manual provide
the detailed steps required to successfully set up and operate the CEM25 mount.
3.2. CEM25 Mount Assembly
NOTE: The CEM25 mount is a precision astronomical instrument. It is highly recommended that you
read the entire manual and become familiar with the nomenclature and function of all components
before starting the assembly.
