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Figure 4.
To center the secondary mirror under the focuser, hold
the secondary mirror holder in place with one hand while adjusting
the center screw with a Phillips screwdriver. Do not touch the mirror's
surface
loosen the three small alignment setscrews in the center
hub of the 4-vaned spider several turns. Now hold the mirror
holder stationary (be careful not to touch the surface of the
mirrors), while turning the center screw with a Phillips head
screwdriver (Figure 4). Turning the screw clockwise will move
the secondary mirror toward the front opening of the optical
tube, while turning the screw counter-clockwise will move the
secondary mirror toward the primary mirror.
Note: Be careful not to bend the spider vanes when making
adjustments to the secondary mirror.
When the secondary mirror is centered in the focuser draw-
tube, rotate the secondary mirror holder until the reflection
of the primary mirror is as centered in the secondary mirror
as possible. It may not be perfectly centered, but that is OK.
Now tighten the three small alignment set screws equally to
secure the secondary mirror in that position.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 3c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosen-
ing one of the three alignment setscrews while tightening the
other two, as depicted in Figure 5. The goal is to center the
primary mirror reflection in the secondary mirror, as in Figure
3d. Don't worry that the reflection of the secondary mirror
(the smallest circle, with the collimation cap "dot" in the cen-
ter) is off-center. You will fix that in the next step.
aligning the Primary Mirror
The final adjustment is made to the primary mirror. It will
need adjustment if, as in Figure 3d, the secondary mirror is
centered under the focuser and the reflection of the prima-
ry mirror is centered in the secondary mirror, but the small
reflection of the secondary mirror (with the "dot" of the col-
limation cap) is off-center.
To access the primary mirror collimation screws, remove
the cover plate on the rear end of the optical by unthread-
ing the three Phillips-head screws with a screwdriver. The
tilt of the mirror is adjusted with three pairs of collimation
screws (Figure 6). The collimation screws can be turned with
a Phillips head screwdriver and a 2.5mm Allen wrench.
Figure 5.
Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with a 2mm Allen wrench.
Figure 6.
The back end of the optical tube (bottom of the primary
mirror cell). The three pairs of set screws and Phillips-head screws
adjust the tilt of the primary mirror.
Each pair of collimation screws work together to adjust the
tilt of the primary mirror. The set screw pushes the mirror for-
ward while the Phillips head screw pulls the mirror cell back.
One must be loosened and the other tightened by the same
amount in order to adjust the tilt. Try tightening and loosening
one of the pairs of collimation screws one turn. Look into the
focuser and see if the secondary mirror reflection has moved
closer to the center of the primary. You can tell this easily with
the collimation cap and mirror center mark by simply watch-
ing to see of the "dot" of the collimation cap is moving closer
or farther away from the ring on the center of the primary mir-
ror. Repeat this process on the other two pairs of collimation
screws, if necessary. It will take a little trial and error to get a
feel for how to adjust the mirror to center the "dot" of the col-
limation cap in the ring of the mirror mark.
When you have the dot centered as much as possible in the
ring, your primary mirror is collimated. The view through the
collimation cap should resemble Figure 3e. Make sure all
the collimation screws are tight (but do not overtighten), to
secure the mirror tilt.
A simple star test will tell you whether the optics are accu-
rately collimated.
Set screw
Phillips-head
screw
7
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