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4. Collimation
(Aligning The Mirrors)
Collimation is the process of adjusting the mirrors so
they are perfectly aligned with one another.
Your telescope’s optics were aligned in our work-
shops, and should not need much adjustment unless
the telescope was handled roughly during shipment.
Accurate alignment is important to ensure the peak
performance of your telescope, so it should be
checked regularly. Collimation is relatively easy to
do and can be done in daylight. To check the
collimation, remove the eyepiece and look down the
focuser drawtube. You should see the secondary
mirror centered in the drawtube as well as the
reflection of the primary mirror centered in the
secondary mirror, and the reflection of the
secondary mirror (and your eye) centered in the
reflection of the primary mirror, as in Figure 12a.
If anything is off-center, as in Figure 12b, proceed
with the following collimation procedure It helps to
put a piece of white paper on the inside of the
optical tube opposite the focuser. It forms a bright
background behind the secondary mirror, making it
easier to distinguish the mirror holder from the
background.
Use a Collimating Tool
To aid in centering your line of sight down the
focuser drawtube, and in centering the mirror
reflections during collimation, it is very helpful to use
a precision collimating tool containing crosshairs,
such as the Orion Collimating Eyepiece (#3640).
We strongly recommend that you purchase one.
Alternatively, you can make a crude collimating tool
out of an empty, black plastic 35mm film canister.
It will not have crosshairs, so it won’t be as precise,
but it will be better than nothing. Cut 1/2" from the
top lip of the canister and put a 1/16" to 1/8"
diameter hole in the center of its bottom. The film
canister collimating tool goes into the focuser like an
eyepiece, with the bottom end out.
The Bintel Deluxe Laser Collimator can also be used.
It comes with it’s own instruction manual.
Aligning the Secondary Mirror
With eyepiece removed, look straight down the
open focuser drawtube at the secondary (diagonal)
mirror. Ignore the reflections for the time being.
The secondary mirror itself should be centered in the
focuser drawtube, in the direction parallel to the
length of the telescope. If it isn’t, as in Figure 14b,
it must be adjusted. (It helps to adjust the
secondary mirror in a brightly lit room with the
telescope pointed toward a bright surface, such as
white paper or a wall.) Loosen the three small
alignment screws in the center hub of the secondary
mirror holder several turns. Now hold the secondary
mirror holder stationary (be careful not to touch the
surface of the secondary mirror!), while turning the
center Phillips head screw (as in Figure 13).
Turning the bolt clockwise will move the secondary
mirror toward the front opening of the optical tube,
while turning the bolt counter-clockwise will move
the secondary mirror toward the primary mirror.
When the secondary mirror is centered in the focuser
draw-tube, rotate the secondary mirror holder slight-
ly until the reflection of the primary mirror is as cen-
tered in the secondary mirror as it will get. It still
may not be perfectly centered, but that is OK.
Now tighten the three alignment screws to secure
the secondary mirror in that position. This
adjustment will rarely need to be done, if ever.
Figure 12a When all optical elements are collimated
the view through the focuser should look like this.
Figure 12b All elements
are out of alignment
Figure 12c Secondary is
centered under focuser but
needs adjustment.
Figure 12d Secondary is
collimated
but
primary
needs adjustment
Figure 13 Adjust the tilt of the secondary mirror by adjusting
the three alignment screws with a Phillips head screwdriver
