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position. Then, if necessary, make adjustments to these 3 Phillips-head
screws to refine the tilt-angle of the diagonal mirror until the entire primary
mirror can be seen centered within the diagonal mirror reflection. When the
diagonal mirror is correctly aligned, it will look like
Fig. 9. (Note: the primary
mirror is shown out of alignment.)
c. Primary mirror adjustments
If the diagonal mirror (1, Fig. 9) and the reflection of the primary mirror (2,
Fig. 9) appear centered within the drawtube (3, Fig. 9), but the reflection of
your eye and the reflection of the diagonal mirror (
4, Fig. 9) appear off-
center, you will need to adjust the primary mirror tilt Phillips-head screws of
the primary mirror cell (3, Fig. 6). These primary tilt screws are located behind the primary mirror, at the
lower end of the main tube. See
Fig. 4. To adjust the primary mirror tilt screws, first unscrew several turns,
the 3 hex-head primary mirror cell locking screws (2, Fig.6) that are next to each primary mirror tilt Phillips-
head screw. Then by trial-and-error, turn the primary mirror tilt Phillips-head screws (3, Fig. 6) until you
develop a feel for which way to turn each screw to center the reflection of your eye. Once centered, as in
Fig. 7, turn the 3 hex-head primary mirror cell locking screws (2, Fig. 6) to relock the tilt-angle adjustment.
d. Star testing the collimation
With the collimation performed, you will want to test the accuracy of the alignment on a star. Use the 25mm
eyepiece and point the telescope at a moderately bright (second or third magnitude) star, then center the
star image in the telescope’s field-of-view. With the star centered follow the method below:
• Bring the star image slowly out of focus until one or more rings are visible around the central disc. If
the collimation was performed correctly, the central star disk and rings will be concentric circles, with a
dark spot dead center within the out-of-focus star disk (this is the shadow of the secondary mirror), as
shown in Fig. 10C. (An improperly aligned telescope will reveal elongated circles (Fig. 10A), with an
off-center dark shadow.)
• If the out-of-focus star disk appears elongated (Fig. 10A), you will need to adjust the primary mirror
Phillips-head tilt screws of the primary mirror cell (3, Fig. 6).
• To adjust the primary mirror tilt screws (3, Fig. 6), first unscrew several turns the 3 hex-head primary
mirror cell locking screws (2, Fig. 6), to allow free turning movement of the tilt knobs.
• Using the flexible cable controls (3 and 4, Fig. 1e), move the telescope until the star image is at
the edge of the field-of-view in the eyepiece, as in Fig. 10B.
• As you make adjustments to the primary mirror tilt screws (
3, Fig. 6), you will notice that the out-of-
focus star disk image will move across the eyepiece field. Choose one of the 3 primary mirror tilt screws
and slightly move the shadow to the center of the disk. Then slightly move the telescope using the
flexible cable controls to center the star disk image in the center of the eyepiece.
• If any further adjustments are necessary, repeat this process as many times as needed until the out-
of-focus star disk appears as in Fig. 10C, when the star disk image is in the center of the eyepiece
field.
• With the star testing of the collimation complete, tighten the 3 hex-head primary mirror locking screws
(2, Fig. 6).
2
Fig. 5: Diagonal Assembly.
3
2
Fig. 6: Primary Mirror Cell.
1
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