Leisure Time LX20 - Manual (Page 19)

9. HI-PRECISION: The High-Precision Pointing feature of
LX200 allows for very precise pointing of the telescope. By
incorporating the unique LX200 SYNC command, 0.3 arc-
sec resolution encoders, and high-speed DC servo motors,
observers can now place objects in the telescope's field of
view with 1 arc-minute or better pointing accuracy. This
makes critical image placement applications, such as CCD
imaging, possible.
Normal telescope pointing accuracy is better than 5 arc-
minutes when doing a casual alignment, which is more than
accurate enough for most observing applications. (A "casual"
alignment is one that uses the UNKNOWN SITE or one that
is done without the use of a reticle eyepiece to exactly
center the alignment stars.) This type of alignment will put
objects into the field of view of most eyepieces and is more
than adequate for almost any visual observing application.
A "critical" alignment will improve the pointing accuracy of
the telescope to 2 arc-minutes or better. This type of
alignment requires accurate SITE information, time, date,
proper selection of the two alignment stars, and a reticle
eyepiece to exactly center the alignment stars. These steps
generally require only a few extra seconds to accomplish,
and will improve the telescope's positioning by a substantial
amount. Using the "critical" alignment will provide telescope
positioning suitable for all but the most demanding pointing
applications — including CCD imaging with larger chip
cameras, like the Meade Pictor 416 and Pictor 1616 CCD
cameras.
The HI-PRECISION feature increases the pointing
accuracy of the LX200 to 1 arc-minute or better and also
requires the "critical" alignment described above. This will
yield the best pointing accuracy possible, placing objects
onto the active area of the even the smallest CCD cameras
available.
It should be stressed that for most applications, using the
HP feature is NOT required to get maximum enjoyment out
of the telescope. For an evening of simple visual
observations, the "casual" alignment is all that is required.
Don't let the pointing precision of the telescope become more
important than the fun of observing the night sky!
The High-Precision Pointing mode requires the "critical"
alignment, described above, to maximize the telescope's
pointing ability. The LX200 default condition is with HP
disabled. To activate the HP mode, select the "hi-precision"
option from the TELESCOPE menu (option #9). When
selected, "HI-PRECISION" will change to upper case letters.
When HP is active, the LX200 automatically does several
things whenever a GO TO is initiated.
a. HP will search the alignment star database and find the
three closest stars to the object (or position) entered.
This process takes about 10 seconds and the keypad
will show Display 26:
NOTE: If this star is not in the field of view or if it is obstructed
by a land object, the other two stars are available. Use the
PREV and NEXT keys to cycle through the three closest stars.
c. The telescope will slew to the selected object or position.
10. SLEW RATE: Option #10 in the TELESCOPE menu is for
changing the slew rate of the LX200 telescope. Slowing down
the slew rate will result in less noise as the telescope moves
and will also use a little less power. To change the slew rate,
follow these steps:
a. Press the MODE key on the keypad until the
TELESCOPE/OBJECT LIBRARY menu appears. The
cursor should be next to the TELESCOPE option — if
not, press the PREV key to move the cursor up one
space.
b. Press ENTER to select the TELESCOPE functions.
c. Press the PREV or NEXT keys to move the cursor to
option #10: SLEW RATE. On the right hand part of
the display, the number 4 is displayed. This
represents the current slew rate in degrees per
second.
d. Press the ENTER key to change the slew rate. Each
successive ENTER key press increments the slew rate
by 1 degree per second.
e. After setting the desired rate, press the MODE key to
return to the TELESCOPE/OBJECT LIBRARY menu.
NOTE: The slew rate is NOT stored in permanent memory and
needs to be reset each time the telescope is powered up. The
default slew rate is 4 degrees per second.
11. BACKLASH: The Backlash feature is only available in the
POLAR mode.
When taking long exposure astrophotographs, it is
necessary to "guide" the photograph to make sure the
telescope is tracking perfectly, otherwise stars will appear as
ovals instead of pinpoints. This is done by setting the LX200
keypad to the GUIDE speed, monitoring the star location
(e.g. with an off-axis guider), and making small
corrections to the telescope position by using the N, S, E,
and W keys.
When making these corrections, the R.A. motor will speed
up or slow down (by pressing the "E" and "W" keys). The
Declination motor, however, when activated (by pressing the
"N" and "S" keys) will actually stop and reverse direction.
Because of backlash in the Declination motor gearbox, there
will be a few seconds delay before the
telescope begins to move when reversing direction.
The Dec. backlash feature compensates for the Dec. motor
gearbox backlash and provides instant telescope movement
when the motor is reversed.
To program the Dec. backlash, use this procedure:
a. Move to option #11 from the TELESCOPE menu.
The keypad display will show:
'"11) BACKLASH 00"
The "00" in the display shows the number of arc-
seconds of backlash the LX200 is set to compensate
for (the default setting is 0 arc-seconds).
b. While observing a star at high power, time the
Declination movement delay when reversing the motor
directions (by pressing the "N" and "S" keys). Typical
values are 2 to 4 seconds.
c. The GUIDE speed for the Declination motor is 15 arc-
seconds per second. Therefore, multiply the
number of seconds delay by 15.
d. Press and hold the ENTER key for 1 second. The
keypad will beep and a blinking cursor will appear on
the keypad display. Enter the number determined in
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b. The telescope will slew to the nearest alignment
star. These are all bright (brighter than 3rd
magnitude) stars and far enough apart to insure
that there will only be one in the field of view. The
keypad display will show Display 27:
using a reticle eyepiece, center tne star in tne neia or
view. (Or center the star on the CCD chip if using a
CCD camera.) Press GO TO when the star is centered.