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7
Secondary Mirror Adjustment
If the view looks something like the following figure
with the dot of the collimation eyepiece NOT centered
in the secondary center ring, the secondary mirror
needs be adjusted.
There are three collimation set-screws at the front of
the secondary mirror holder. This will adjust the tilt of
the secondary, changing the relative position of the
secondary center ring when peering through the
collimation eyepiece.
NOTE: DO NOT adjust the center screw! Only
adjust the three screws around the perimeter of
the holder! Adjusting the center screw can cause
the secondary mirror to fall off and will not be
covered under warranty.
A 4mm hex key is needed to perform collimation on
the secondary mirror. When one of these screws is
adjusted counter-adjustments need to be made to the
other two. In other words, if one screw is loosened
the other two need to be tightened, and vice versa. At
the end of the process all three collimation screws
should be reasonably tight so the secondary mirror
won’t shift while the scope is in use.
Always start by loosening one screw. Adjust the
screws only very slightly—by no more than 1/8 turn at
a time, and one screw at a time before checking the
view through the Cheshire again to see how things
changed. Only tiny adjustments should be required to
achieve collimation. This will also aid in the
prevention of accidently putting the telescope grossly
out of collimation. With each tiny tweak of a screw,
make a mental note of which way and how far the
center dot moved, as that will inform which screw to
turn next and by how much. Experiment with different
combinations of loosening / tightening the three
screws one by one until the collimation eyepiece’s
black dot is centered in the dark ring of the secondary
mirror. The correct alignment of the secondary mirror
is critical in determining if the optical axis requires
alignment. Be sure the secondary mirror is properly
aligned before proceeding to the next step.
Optical Axis (Primary Mirror) Adjustment
After done secondary mirror adjustment, if the optical
axis, which is denoted by a thin outline of light (white)
around the perimeter of the view through the
collimating eyepiece, is not a perfect circle of uniform
thickness, that means the optical axis (primary mirror)
needs adjustment. A 3mm and a 2.5mm hex key are
required for the 6" and 8" telescopes, and a 4mm and
a 2.5mm hex key are required for the 10" telescope.
There are total three pairs of screws on the rear cell
of the optical tube where the focuser attaches. Each
pair consists of a small black screw and a larger
chrome screw.
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