Apertura Dobsonian Telescope, Owner'S Manual

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the shape of the secondary mirror is actually oval, when properly aligned it will
appear to be circular as viewed through the focuser.
3.
Insert the laser collimator into the 2” adapter sleeve and then insert that into the
focuser. Secure the laser collimator with the thumbscrew. Turn on the laser
collimator and rotate its target face toward the back end of the scope (the
primary mirror end).
4.
Hold up a piece of paper in front of the telescope to see if the laser is missing the
secondary mirror on reflection. If the laser isn’t reflected onto the paper, then
most likely it is hitting the secondary mirror as it should.
5.
Carefully peer into the tube to see where the laser is hitting the primary mirror
below.
CAUTION: Do NOT allow the laser to shine directly into your eye from the
telescope’s mirrors . The laser should be shining in the middle of the small donut
ring in the middle of the primary mirror. If it is not, adjust the tilt of the secondary
mirror using the three small screws on the top of the secondary mirror assembly
until the laser is centered in the donut ring on the primary.
6.
Now view the target face on the laser collimator to see if the laser is hitting
anywhere on the target face. If not, then this simply means that the primary
mirror is far enough out of adjustment that the laser is outside the target
face on the collimator. In either case, you will need to move to the bottom end of
the scope and loosen the large white locking knobs. Then adjust the angle of the
primary mirror with the large black adjustment knobs until the laser becomes
centered in the hole in the middle of the laser collimator’s target face.
7.
Once accomplished, lock the primary mirror assembly with the white knobs. This
may cause some minor movement of the mirror, so continue fine adjustments
until all six knobs are firm and the laser is centered on its target.