Celestron FirstScope 76mm f/4 Signature Series Moon Alt-Az Reflector Telescope User Manual
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Aligning the Secondary Mirror
If you have an eyepiece in the focuser, remove it. Rack the focuser tube in completely, using the focusing knobs,
until its silver tube is no longer visible. You will be looking through the focuser at a reflection of your eye in the
secondary mirror superimposed on the primary mirror (Figure 6-2). If the primary mirror is not centered in the
secondary mirror, adjust the secondary mirror screws by alternately tightening and loosening them until the mirror is
centered.
Both mirrors aligned with your eye looking into the focuser.
Figure 6-2
Figure 6-3
Even though the star pattern appears the same on both sides of focus, they are asymmetric. The
dark obstruction is skewed off to the left side of the diffraction pattern indicating poor
collimation.