Orion starBlast 4.5 EQ - Manual (Page 11)

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Once the secondary mirror is centered in the focuser drawtube,
and the primary mirror reflection is centered in the secondary
mirror, the secondary mirror is properly aligned, and no further
adjustments to it should be needed.
aligning the Primary Mirror
The final adjustment is made to the primary mirror. It will need
adjustment if, as in Figure 9d, the secondary mirror is centered
in the focuser drawtube and the reflection of the primary mir-
ror is centered in the secondary mirror, but the small reflection
of the secondary mirror (with the “dot” of the collimating cap) is
off-center.
The tilt of the primary mirror is adjusted with the three large
knurled thumbscrews on the rear end of the optical tube (back of
the mirror cell) (Figure 13). The small thumbscrews (with slots in
them) serve to lock the mirror in place. Start by loosening each
of these smaller thumbscrews a few turns. Use a screwdriver in
the slots, if necessary. Now adjust the tilt of the primary mirror by
turning one of the large thumbscrews either clockwise or coun-
terclockwise. Look into the focuser and see if the secondary mir-
ror reflection has moved closer to the center of the primary mirror
reflection. You can determine this easily with the collimating cap
and primary mirror center mark by simply watching to see if the
“dot” of the collimating cap is moving closer or farther away from
the “ring” on the primary mirror. If it isn’t getting closer, try turning
the thumbscrew in the opposite direction. Repeat this process
for the other two large thumbscrews, if necessary. It will take a
little trial-and-error to get the feel for how to adjust the primary
mirror to center the dot of the collimating cap in the ring of the
primary mirror center mark.
When you have the dot centered as much as possible in the
ring, your primary mirror is aligned. The view through the col-
limating cap should resemble Figure 9e. Make sure the smaller
thumbscrews on the back of the mirror cell are tightened to lock
the primary mirror in position.
A simple star test will tell you whether the optics are, in fact,
accurately aligned.
star‑testing the telescope
When it is dark, point the telescope at a bright star and accu-
rately center it in the eyepiece’s field of view. Slowly de-focus the
image with the focus knob. If the telescope’s optics are correctly
aligned, the expanding disk should be a perfect circle (Figure
14). If the image is unsymmetrical, the optics are out of align-
ment. The dark shadow cast by the secondary mirror should
appear in the very center of the out-of-focus circle, like the hole
in a donut. If the “hole” appears off-center, the optics are out of
alignment.
If you try the star test and the bright star you have selected is not
accurately centered in the eyepiece, the telescope will appear
to need collimating, even though the optics may be perfectly
aligned. It is critical to keep the star centered, so over time you
will need to make slight corrections to the telescope’s position in
order to account for the sky’s apparent motion.
7. astronomical observing
For many, this will be the first foray into the exciting world of ama-
teur astronomy. The following information and observing tips will
help get you started.
choosing an observing site
When selecting a location for observing, get as far away as pos-
sible from direct artificial light such as street lights, porch lights,
and automobile headlights. The glare from these lights will great-
ly impair your dark-adapted night vision. Set up on a grass or
dirt surface, not asphalt, because asphalt radiates more heat.
Heat disturbs the surrounding air and degrades the images seen
through the telescope. Avoid viewing over rooftops and chim-
neys, as they often have warm air currents rising from them.
Similarly, avoid observing from indoors through an open (or
closed) window, because the temperature difference between
the indoor and outdoor air will cause image blurring and distor-
tion.
If at all possible, escape the light-polluted city sky and head for
darker country skies. You’ll be amazed at how many more stars
and deep-sky objects are visible in a dark sky!
“seeing” and transparency
Atmospheric conditions vary significantly from night to night.
“Seeing” refers to the steadiness of the Earth’s atmosphere at a
given time. In conditions of poor seeing, atmospheric turbulence
causes objects viewed through the telescope to “boil”. If you look
up at the sky and stars are twinkling noticeably, the seeing is
poor and you will be limited to viewing at lower magnifications. At
higher magnifications, images will not focus clearly. Fine details
on the planets and Moon will likely not be visible.
In conditions of good seeing, star twinkling is minimal and images
appear steady in the eyepiece. Seeing is best overhead, worst
at the horizon. Also, seeing generally gets better after midnight,
Figure 13. The
tilt of the primary
mirror is adjusted
by turning the three
larger thumbscrews.
Figure 14. A star
test will determine
if the telescope's
optics are properly
collimated.
An
unfocused view of a
bright star through
the eyepiece should
appear as illustrated on the right if optics are perfectly collimated. If
the circle is unsymmetrical, as illustrated on the left, the scope needs
collimation.
Out of collimation Collimated