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14 I ENGLISH
COLLIMATING THE OPTICS
Collimation is the process of aligning the telescope’s optics.
Dobsonians use the Newtonian reflector optical design,
which consists of a parabolic primary mirror and a flat
secondary mirror. To ensure best performance, you should
periodically check the alignment of the optics. To help with
this, we have included a special “collimation cap” you can
use. In addition, the primary mirror is center-marked with an
adhesive ring label to aid in collimation.
To check alignment of the mirrors, first remove any
eyepieces. Make sure the 2”-to-1.25” adapter is installed in
the focuser. Then, place the collimation cap in the focuser
(Figure 15).
Figure 15: To check the alignment of the mirrors, use the included
collimation cap in the focuser.
Look through the small hole in the center of the collimation
cap. The view should look like Figure 16. If it does not, you’ll
need to make some adjustments to the mirrors’ alignment.
Bottom edge
of focuser
drawtube
Reflection of
your eye
Edge of
secondary
mirror
Secondary
mirror
holder
Primary
mirror clip
Reflection of
secondary mirror holder
Figure 16: If your telescope is properly aligned, the view through the
collimation cap should look like the drawing above.
It is easiest to collimate a telescope during the day with
the telescope pointed toward a blank wall. This will provide
a high-contrast view, making it easier to determine which
adjustments should be made. Use the supplied hex key(s)
to make adjustments. The 8” SSE Dob comes with 2mm
and 2.5mm hex keys. The 10” SSE Dob comes with a single
2mm hex key. For the 8” SSE Dob, you’ll also need to use
the supplied Phillips head screwdriver.
First, adjust the secondary mirror at the front of the telescope
using the 2mm hex key. While making adjustments, we
recommend positioning the tube horizontally. This prevents
anything from falling onto the primary mirror.
1. You should be able to see the reflection of the entire
primary mirror centered within the secondary mirror as
shown in Figure 16. If you can’t (like in Figure 17, for
example), use the three socket-head set screws in the
secondary mirror holder to adjust the tilt of the secondary
mirror (Figure 18).
Edge of
secondary
mirror
Reflection of
primary mirror
Figure 17: If the reflection of the primary mirror is not centered within
the secondary mirror as shown above, you will need to adjust the tilt of
the secondary mirror.
2mm
Hex key
Figure 18: The three socket head set screws in the secondary mirror
holder adjust the tilt of the secondary mirror.
Reflection
of primary
mirror
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