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page 36
Star testing the collimation
With the collimation performed, you will want to test the accuracy of the alignment on
a star. Use the H 25mm eyepiece and point the telescope at a moderately bright (sec-
ond 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 C, Fig. 29. (An
improperly aligned telescope will reveal elongated circles (A, Fig. 29), with an off-
center dark shadow.)
• If the out-of-focus star disk appears elongated (B, Fig. 29), you will need to adjust
the primary mirror Phillips-head tilt screws of the primary mirror cell (3, Fig. 24).
• To adjust the primary mirror tilt screws (3, Fig. 24), first unscrew several turns the
three hex-head primary mirror cell locking screws (2, Fig. 24), to allow free turning
movement of the tilt knobs.
• As you make adjustments to the primary mirror tilt screws (3, Fig. 24), you will
notice that the out-of-focus star disk image will move across the eyepiece field.
Choose one of the three primary mirror tilt screws that will move the star disk
image to the center of the eyepiece field.
• Repeat this process as many times as necessary until the out-of-focus star disk
appears as in C, Fig. 29, when the star disk image is in the center of the eyepiece
field.
• With the star testing of the collimation complete, tighten the three hex-head
primary mirror locking screws (2, Fig. 24).
Fig. 29: Collimation.
ABC