drawtube
Reflection of primary mirror clip
Reflective surface | Primary mirror |
of collimation | center mark |
cap |
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b.c.
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d. |
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Figure 27. 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, if the optics are out of alignment, the view might look something like this.
(c)Here, the secondary mirror is centered under the focuser, but it needs to be adjusted (tilted) so that the entire primary mirror is visible. (d) The secondary mirror is correctly aligned, but the primary mirror still needs adjustment. When the primary mirror is correctly aligned, the center “dot” of the collimation cap will be centered, as in (e).
Appendix A: Collimating the Optics
Collimating is the process of adjusting the mirrors so they are aligned with one another. Your telescope’s optics were aligned at the factory, and should not need much adjustment unless the telescope was handled roughly in transit. Accurate mirror align- ment is important to ensure the peak performance of your tele- scope, so it should be checked regularly. Collimating is a rela- tively easy process and can be done in daylight or darkness.
To check collimation, remove the eyepiece and look down the focuser drawtube. You should see the secondary mirror cen- tered 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 27a. If anything is
The Collimation Cap
Your StarBlast 6/6i comes with a “quick collimation cap” (Figure 28). This is a simple cap that fits on the focuser drawtube like a dust cap, but has a tiny hole in the center and a reflective inner surface. The collimation cap helps center your eye over the focuser drawtube so that aligning the optical components is easier to achieve. The reflective surface provides a distinct visual reference that is helpful in centering the mirror reflec- tions. Figures 27b through 27e assume that you have the col- limation cap in place.
Figure 28. The quick collimation cap, which features an inner reflective surface, helps in centering reflections of the optics in the focuser during the collimation process.
The Primary Mirror Center Mark
You’ll notice that the primary mirror of the StarBlast 6/6i has a tiny ring (sticker) marking its center. This “center mark” allows you to achieve a very precise collimation; you don’t have to guess where the exact center of the mirror is.
NOTE: The center ring sticker need not ever be removed from the primary mirror. Because it lies directly in the shadow of the secondary mirror, its presence in no way adversely affects the optical performance of the telescope or the image quality. That might seem counterintuitive, but it’s true!
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