12
Aligning the Mirrors
(Collimation)
Collimation is the process of adjusting the optics of a telescope
so they are precisely aligned with one another and with the tele-
scope tube. For this reflector telescope, the primary and second-
ary mirrors must be in precise alignment. Your telescope’s optics
were aligned at the factory, and should not need much or any
adjustment unless the telescope is handled roughly. Accurate
mirror alignment is important to ensure the sharpest possible
images viewed through your telescope, so it should be checked
occasionally. With practice, collimating is relatively easy to do
and can be done in daylight.
It helps to perform the collimation procedure in a brightly lit room
with the telescope pointed toward a bright surface, such as a
light-colored wall. The telescope tube should be oriented hori-
zontally (parallel to the ground). Placing a piece of white paper
in the telescope tube opposite the focuser (i.e., on the other
side of the secondary mirror from the focuser) will also be help-
ful (see
Figure 28
). You will need the included screwdriver with
the Philips bit to perform the collimation.
To check your telescope’s collimation, remove the eyepiece and
look down the focuser. You should see the secondary mirror
centered in the focuser, 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 29A
. Got all that? Review it again
carefully, and compare what you see to
Figure 29A
. If anything
is off-center, proceed with the following collimation procedure.
NOTE:
Precise collimation is best achieved by using an optional
collimating tool, such as a quick-collimation cap, a Cheshire
eyepiece, or a laser collimator. Check our website for available
collimating tools.
Figures 29B
through
29D
assume that you
have an optional Cheshire eyepiece or collimation cap in the
focuser.
Primary Mirror Center Mark
You may have noticed that your SkyScanner BL has a small
adhesive dot in the exact center of the primary mirror. This
“center mark” allows you to achieve a very precise collimation
of the primary mirror; you don’t have to guess where the center
of the mirror is, which is important in the collimation process.
This center mark is especially useful when using an optional
collimating device.
Note:
The adhesive dot should not be removed from the primary
mirror. Because it lies directly in the shadow of the second-
ary mirror, its presence in no way adversely affects the optical
performance of the telescope or the image quality. That might
seem counter-intuitive, but it’s true! Leave it in place.
Aligning the Secondary Mirror
Align the secondary mirror first. Note that for the SkyScanner
BL 102mm the secondary mirror collimation screws are Philips
head screws, so you will need to use the Philips screwdriver to
adjust them. The SkyScanner BL 135mm model’s secondary
mirror collimation screws are thumbscrews, so you use your
fingers to adjust them.
Look down the focuser at the secondary (diagonal) mirror. If the
entire primary mirror reflection is not visible in the secondary
Figure 29.
Collimating the optics.
(A)
When the mirrors are properly aligned, the view down the focuser drawtube should look like this.
(B)
With the collimation cap in place, (with a collimation cap or Cheshire eyepiece in place). Here, only part of the primary mirror is visible in the
secondary mirror, so the secondary mirror needs to be adjusted (tilted).
(C)
Here the secondary mirror is correctly aligned because the entire
primary mirror is visible in it. But the reflection of the secondary mirror is off-center. So the primary mirror still needs adjustment.
(D)
Now the
primary mirror is correctly aligned, so the secondary mirror is centered.
A.
B.
C.
D.
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