Periodic Error Correction - Meade LX200GPS Instruction Manual

Periodic Error Correction

If you wish to perform high-precision astrophotography, you may wish to "train" your
telescope in order to keep objects that you are imaging dead center in the telescope's
mirror during the photographic exposure. Periodic error correction (PEC) helps to
remove the slight perturbations from center that occur due to the mechanical nature
of a telescope. To perform this procedure, you need to use a high-power reticle, such
as the 9mm reticle (see
OPTIONAL ACCESSORIES
for both drives.
Train Menu Option
If you perform this procedure in alt/az alignment, you can train the telescope in both
the R.A. and the Dec. axes; in polar alignment, you need only train the telescope's
R.A. axis. If you train the telescope in polar alignment, make sure that "Polar" is
selected in the "Telescope: Mount" menu ("Alt/Az" is the default setting).
To perform the procedure on the Dec. axis, pick a bright star in the East or West that
is about about 20° above the horizon.
To perform the procedure on the R.A. axis, pick a bright star in the South that has min-
imal movement and is about 30° above the horizon (Note: If in the Southern hemi-
sphere, pick a star in the North that is about 30° above the horizon).
Important Note: The Train option overwrites any previous PEC data.
1. Select "Train" from the Dec. PEC menu (in the "Setup: Telescope" menu) and press
ENTER.
2. Look through the reticle. Use the Arrow keys to keep the star centered in the reticle
cross-hairs. Autostar II displays a count of the 200 positions of the worm gear. When
the count reaches 200, one cycle is complete. A full cycle takes about 8 minutes.
3. Select "Train" from the R.A. PEC menu (in the "Setup: Telescope" menu) and press
ENTER.
4. Look through the reticle. Use the Arrow keys to keep the star centered in the reticle
cross-hairs. Autostar II displays a count of the 200 positions of the worm gear. When
the count reaches 200, one cycle is complete. A full cycle takes about 8 minutes.
5. Press MODE to exit.
Update Menu Option
Use the Update option to further refine your training; it is recommended that you
update your original training two or three times when first using your telescope.
Update does not overwrite the data, but updates the training using information gath-
ered from both the last and the current training sessions. Press the MODE key to exit
from this option. If you wish to further refine your training, select this menu again and
repeat the procedure.
Erase Menu Option
Select this option to erase all PEC training data.
On and Off Menu Options
Select "On" when you want the telescope to use the training information. Select "Off"
when you do not want for the telescope to use the training information. Select "On" to
enable the Smart Drive.
, page 42). PEC training is available
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