Paramount GEM User Guide
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Mount Slew Limits
The typical mechanical orientation of a GEM is when the optical tube assembly end of the declination axis is on
one side of the pier when the observed object is on the opposite side of the meridian. In this orientation, the end
of the counterweight shaft that holds the counterweights is below horizontal and the mount’s payload cannot
collide with the side of the pier, so there is little risk of damaging your equipment.
Operating a GEM in an “atypical” orientation (see Figure 72), that is, when the optical tube assembly end of the
declination axis and the observed object are on the same side of the meridian, offers several advantages:
• An observed object can be tracked across the meridian without having to flip sides during the exposure.
This maintains the orientation of the field of view. For a GEM, when the OTA changes sides of the pier,
the image plane to rotate 180 degrees.
• Guide stars do not have to be reacquired. Flipping sides requires reacquisition of the guide star when the
mount slews to the other side of the pier.
However, the significant disadvantage of operating a GEM in an atypical orientation is that the mount’s payload
can collide with the side of the pier. While the Paramount’s motors are current limited, which means that running
into a fixed object will automatically stop slewing and tracking, it is always best to keep your optical equipment
from running into anything.
The Mount Slew Limits options allow the Bisque TCS software limits to be configured such that the payload of a
GEM cannot encounter the side of the pier.
After mounting the payload (camera, optical tube assembly and other equipment) to the Versa-Plate, use the
hand controller or joystick to orient the mount in the atypical GEM orientation. The counterweight end of the
counterweight shaft will be above horizontal, and the payload will run into the side of the pier at some
declinations.
To properly configure the software slew limits the mount must be oriented at the maximum slew position in both
hour angle and declination. Start by turning tracking off (choose the Turn Tracking Off command from the Tools
pop-up menu on the Telescope window) to ensure the mount stays at the limit position.
Next, use the hand controller or joystick to carefully slew the hour angle axis until the mount is in the atypical
position, without running the equipment into the side of the pier. You know the hour angle axis is oriented at the
maximum slew position after slewing the declination axis 180 degrees always clears the side of the pier; we
recommend a minimum of 1 inch (2-3 cm).
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