Meade Instruments LX850 - Manual (Page 26)

StarLock Automatic Rate
Calibration (ARC)
Obtaining best performance from StarLocked telescopes
requires that the guiding aggressiveness be optimally
set for current viewing/imaging conditions. This is an
essential procedure to obtain peak tracking accuracy
Please refer to Appendix C, page 53 for details.
Periodic Error Correction
Training the mount using AutoStar's built-in Periodic
Error Correction is necessary to achieve peak
performance of the LX850 Telescope System.
This is especially true when you are taking long
exposure photography.
Periodic Error Correction should be done after you
have fully assembled your mount, balanced with all the
auxiliary equipment you plan on using and you have
successfully aligned the telescope. It is also important
that this performed under reasonably dark skies with
good seeing conditions. If atmospheric conditions are
poor you will not obtain accurate error correction. See
page 43 for directions on how to perform the Periodic
Error Correction routine.
StarLock And Mount Flexure
The StarLock is normally attached to the saddle plate of
your mount. When enabled, it waits a few seconds after
the completion of a slew, and then automatically finds a
guide star and begins auto-guiding your telescope. This
assures that your mount will precisely compensate for
the movement of stars across the sky. Provided your
telescope is securely attached to the mount, it too will
track precisely with the movement of stars across the
sky. If the position of your OTA, camera, diagonal or
eyepiece changes over time, you will see a small drift
in the position of objects. This problem is known as
differential flexure.
Meade’s LX850 OTAs have been engineered to limit
flexure sufficiently to make images up to 10 minutes or
longer in duration without any noticeable movement of
objects. Often, depending upon where you are pointed
you can go much longer. If you are experiencing drift
due to flexure, you need to track down what is loose and
tighten it up. Things to check include:
StarLock Mounting
The StarLock’s Dovetail should be centered in the
dovetail bracket with its base flush against the bottom
of the saddle plate. Be sure the dovetail bracket is tight
and no movement of the StarLock is occurring.
Note that 10”, 12” and 14” LX850 ACF optical tubes
include their own StarLock mounting bracket located at
the top of the OTA, towards the rear cell. This second
bracket is the preferred mount location for StarLock as it
minimizes flexure in these long focal length OTAs,
OTA Mounting
Likewise, the OTA’s dovetail plate should be flush
against the Saddle Plate and the Dovetail bracket
should be tight. Additionally, you should check that the
cap head screws securing the dovetail to the telescope
are tight. This includes the plate interface brackets that
connect the OTA to dovetail plate.
Focusers
If you are using a refractor, be sure that the focus lock
is tightened once you have achieved focus. Crayford-
style focusers are secured via pressure on a rolling pin.
Too much force and the scope will not focus, to little and
the focuser tube can shift as you scope tracks around
the sky, especially with a heavy camera hanging off the
end.
Cameras
Be sure your camera is securely attached to the
telescope. Inserting the camera in a draw tube and
tightening a single captive screw is a recipe for image
shift. Draw tubes should have at least two and preferably
three captive screws so the camera cannot shift when
the scope moves about the sky.
Reflecting Telescope Mirrors
If you are using a telescope with primary mirror atop
the LX850 that does not have Meade’s “Zero Shift”
technology, you must lock your mirror, otherwise
as the scope moves about the sky, the different
stresses will cause the mirror to flop making long
exposures impossible.
Heavy OTAs
If you are using a very heavy OTA, near the 90 pound
limit of the LX850’s capacity, it may prove difficult to
prevent differential flexure. If this is the case, you can
improve performance by attaching the StarLock to the
top of your OTA. While this makes it inconvenient to
exchange OTAs, it may resolve many flexure problems.
The orientation of the StarLock should not change. It
should still be square to the Saddle Plate. Attaching
the StarLock to your OTA will mean that it will not only
compensate for star movement relative to the mount,
but star movement relative to the OTA itself.
AutoStar #497 HANDBOX
StarLock And Mount Fle
xure
26