Observing Tips And Techniques - Orion 23013 Instruction Manual

adjusting the tilt of the secondary Mirror
Look in the focuser drawtube and see if the entire reflection of the
primary mirror is visible and precisely centered in the secondary
mirror. It's centered if there is an even ring of space between the
reflection and the edge of the secondary mirror (Figure 4C). If
there isn't, you'll need to adjust the tilt of the secondary mirror. (It
helps to adjust the secondary mirror in a brightly lit room with the
telescope pointed toward a bright white surface, such as white
paper or a wall.)
First, loosen the four socket-head alignment screws in the sec-
ondary mirror holder enough to be able to rotate the holder with
your hand. Now look into the focuser and rotate the holder
slightly one way, then the other, until the reflection of the primary
mirror is as centered in the secondary mirror as it will get. It still
may not be perfectly centered yet, but that's OK. Now secure the
holder in that rotational position by threading the four alignment
screws back in.
If the entire primary mirror reflection still is not visible and cen-
tered in the secondary mirror, adjust the secondary mirror tilt
further by alternately loosening one of the four alignment screws
and tightening the opposite one a turn or so. Remember, the goal
is to center the primary mirror reflection in the secondary mirror,
as depicted in Figure 4C. Don't worry that the reflection of the
secondary mirror (the smallest circle, with the reflection of your
eye in it) and spider are off-center (as also is the case in Figure
4C); you'll fix that in the next step.
adjusting the tilt of the Primary Mirror
The final adjustment is made to the primary mirror. It will need
adjustment if, as in Figure 4C, the secondary mirror is centered
under the focuser and the reflection of the primary mirror is cen-
tered in the secondary mirror, but the small reflection of the
secondary mirror (with your eye inside) is off-center.
The tilt of the primary is adjusted with the three wing nuts at the
bottom of the optical tube, behind the primary mirror. Turn one
wing nut at time, no more than one turn at a time, then look into
the focuser again and see if the secondary mirror reflection has
moved closer to the center of the primary mirror reflection. You'll
soon get a feel for which wing nuts to turn in which direction and
how far, until finally the secondary mirror reflection is dead center.
(It helps to have two people for primary mirror collimation, one to
look in the focuser while the other adjusts the wing nuts.)
The collimation bolts are spring-loaded, so once you achieve the
correct mirror tilt, just leave the wing nuts as they are; the mirror
will remain in the adjusted position.
The view through the Collimating Eyepiece should now resemble
Figure 4D. The secondary mirror is centered in the focuser; the
reflection of the primary mirror is centered in the secondary mirror,
and the reflection of the secondary mirror is centered in the reflec-
tion of the primary mirror.
Your telescope is in precise collimation—optically primed for peak
performance! Once again, confirm the collimation by conducting a
star test.
8
6. observing tips and
techniques
Pick a location away from streetlights and bright yard lighting. Avoid
viewing over rooftops and chimneys, as they often have warm air
currents rising from them, which distorts the image seen in the
eyepiece. Similarly, you should not observe through an open win-
dow from indoors.
"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, when
you look up at the sky with just your eyes, the stars are twinkling
noticeably, seeing is bad and you will be limited to viewing with
low powers (bad seeing affects images at high powers more
severely). Planetary observing may also be poor. Make sure you
are not looking over buildings or any other source of heat; that will
also cause image degradation.
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,
when much of the heat absorbed by the Earth during the day has
radiated off into space.
Especially important for observing faint objects is good transpar-
ency—air free of moisture, smoke, and dust. All tend to scatter
light, which reduces an object's brightness. Transparency is
judged by the magnitude of the faintest stars you can see with the
unaided eye (6th magnitude or fainter is desirable).
cooling the telescope
All optical instruments need time to reach "thermal equilibrium" to
achieve maximum stability of the lenses and mirrors, which is
essential for peak performance. When moved from a warm indoor
location into the cooler outdoor air, a telescope needs time to
cool to the outdoor temperature. The bigger the instrument and
the larger the temperature change, the more time is needed.
For your Premium DSE, allow at least 1 hour for it to equilibrate.
If the scope has to adjust to more than a 40° temperature
change, allow two to four hours. In the winter, storing the tele-
scope outdoors in a shed or garage greatly reduces the amount
of time needed for the optics to stabilize.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on while you
observe, if your eyepieces have enough "eye relief" to allow you to
see the whole field of view. You can try this by looking through the
eyepiece first with your glasses on and then with them off, and see
if the glasses restrict the view to only a portion of the full field. If they
do, you can easily observe with your glasses off by just refocusing
the telescope the needed amount.
let Your Eyes Dark-adapt
Don't expect to go from a lighted house into the darkness of the
outdoors at night and immediately see faint nebulas, galaxies,
and star clusters—or even very many stars, for that matter. Your
eyes take about 30 minutes to reach perhaps 80% of their full
dark-adapted sensitivity. Many observers notice improvements