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Dual Tangent Arm System
The NGT-12.5 includes declination tangent arms on both sides of the mirror tub. The declinati on drive tangent arm
has a tension-adjusting knob designed for normal adjustments during use. The null tangent arm is for stability only
and has no adjusting knob. Its tension is pre-set at the factory and should not be adjusted.
Any further tightening
of this tension can cause damage to the declination motor and void the warranty.
If you determine that the null
tangent arm needs to be adjusted, use the following procedure.
First, loosen the declination drive tangent arm
completely. Slightly release the tension on the null arm then tighten it very slowly until you feel only the slightest
resistance. That is all that is required for this arm to provide the stability it is designed to give.
Remember, do not
over tighten!
Balancing the Telescope
The NGT-12.5 is designed to be balanced when all the standard accessories are in place. This includes the finder
scope, two piggyback camera counterweights, three sliding truss-rod counterweights, the light shroud (or three extra
sliding counterweights) and an eyepiece. When using a CCD camera, rotate the upper nose assembly until the
camera is above the telescope, drop the sliding counterweights to their lowest position on the truss rods and attach
the extra CCD camera counterweight to the bottom of the tub.
Remember, a balanced telescope is a happy
telescope.
Polar Alignment
For a surprisingly accurate and quick polar alignment, simply place the NGT-12.5 base on the ground and point the
latitude adjusting screw at Polaris, or to be more precise, at that point 8/10ths of a degree to the proper side of Polaris
where the true polar axis exists. The screw's reflective surface makes it easy to see in the dark. Take a few steps
back from the base and further assess the alignment. Continue to adjust the base until you are satisfied that the polar
axis is pointing at the pole.
With a little practice this procedure can get you within ½ degree or better of polar
alignment, in only a few seconds.
An azimuth fine adjustment mechanism is provided on the base for small
adjustments.
Azimuth fine adjustment
Importance of the MAX Computer "Dec=0" Setting
The first mechanical setting required by guiding computers (in the two-star alignment or GQ mode) is at zero
declination. This position is very sensitive. The typical etch mark on the declination bearing is about 0.014" wide.
Movements of 0.007" to the left or right of this mark will make a difference in the guiding accuracy. You may wish to
experiment with this setting to find the best position. Remember that it will affect the guiding, but not necessarily the
"warp" factor. The warp factor is affected more by the distance between the two alignment stars. Remember, all
initial alignments are critical for good guiding.
Summary of Contents for NGT-12.5
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