Celestron ADVANCED VX Serie Manual De Uso página 29

This device allows you to photograph and guide through the
telescope simultaneously In addition, you will need a T-Ring
to attach your camera to the off-axis guider
Other equipment needs include an autoguider, which is a
small camera that attaches to the off-axis guider and keeps
your guide star centered while you are imaging with your
main camera Here is a brief summary of the technique
1 Polar align the telescope For more information on polar
aligning, see the Polar Alignment section earlier in
the manual
2 Remove all visual accessories
3 Thread the off-axis guider onto your telescope
4 Thread the T-Ring onto the off-axis guider
5 Mount your camera body onto the T-Ring the same
as you would any other lens
6 Set the shutter speed to the "B" setting
7 Focus the telescope on a star
8 Center your subject in the field of your camera
9 Using your autoguider, find a suitable guide star in the
telescope field This can be the most time-consuming
part of the process
10 Open the shutter using a cable release
11 Monitor your guide star for the duration of the exposure
using the buttons on the hand controller to make the
needed corrections
12 Close the camera's shutter
Periodic Error Correction (PEC)
Periodic Error Correction, or PEC for short, is a system
that improves the tracking accuracy of the drive by reducing
the number of user corrections needed to keep a guide
star centered in the eyepiece PEC is designed to improve
imaging quality by reducing the amplitude of the worm errors
Using the PEC function is a three-step process First, the
Advanced VX mount needs to know the current position of
its worm gear, so it has a reference when playing back the
recorded error Next, you must guide using an autoguider for
at least 10 minutes during which time the system records
the correction you make (It takes the worm gear 10 minutes
to make one complete revolution) This "teaches" the PEC
chip the characteristics of the worm The periodic error of
the worm gear drive will be stored in the PEC chip and used
to correct periodic error The last step is to play back the
corrections you made during the recording phase Keep in
mind, this feature is for advanced astrophotography and still
requires careful guiding since all telescope drives have some
periodic error
Using Periodic Error Correction
Once the telescope has been properly polar aligned, select
PEC from the Utilities menu and select the Record option
Here's how to use the PEC function:
1 Find a bright star relatively close to the object you want
to image
2 Insert the autoguider into the eyepiece holder of your
telescope Orient the guider so that one axis of the
sensor is parallel to the declination axis while the other
is parallel to the R A axis
3 Focus the telescope, and study the periodic movement
4 Plug the autoguider cable into the autoguider port on the
mount's electronics panel
5 To begin recording the drive's periodic error, press the
MENU button and select PEC from the Utilities menu
Use the Up/Down scroll buttons to display the Record
option and press ENTER When you are ready to record,
press the ENTER button again to begin You will have
5 seconds before the system starts to record The first
time each observing session that PEC record or play is
selected, the worm gear must rotate in order to mark its
starting position If the worm gear rotation moves your
guide star outside the field of view of the eyepiece, it will
have to be re-centered before the recording begins
Note: Once the worm gear is indexed, it will not need to
be positioned again until the telescope is turned off To
give yourself more time to prepare for guiding, it may be
necessary to restart PEC recording after the worm gear
has found its index
6 After 10 minutes, PEC will automatically stop recording
7 Point the telescope at the object you want to image and
center the guide star on the illuminated cross hairs You
are ready to play back the periodic error correction
8 Once the drive's periodic error has been recorded, use
the Playback function to begin playing back the correction
for future imaging guiding If you want to re-record the
periodic error, select Record and repeat the recording
processes again The previously recorded information
will be replaced with the current information Repeat
steps 7 and 8 to playback the PEC corrections for your
next object
Does the PEC function make unguided astroimaging
possible? Yes and no For solar (filtered), lunar and
piggyback (up to 200mm), the answer is yes However,
even with PEC, autoguiding is still mandatory for long
exposure, deep sky astroimaging
ENGLISH
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