Meade LX200 CLASSIC Bedienungsanleitung PDF herunterladen (Seite 6)

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to the telescope. This allows programmers who

find errors in the ASCOM driver for a particular

telescope to send the proper commands through

ASCOM.

Popular software such as Cartes du Ciel and

GuideDog use the ASCOM platform.

K3CCDTools2 does not (yet) use ASCOM, but

instead issues MTSCP commands directly to the

LX200-compatible telescopes.

One of the great benefits of the ASCOM platform

is that once a problem with a driver for a given

telescope or mount is solved in ASCOM, that fix

will be applied to all software installed on a user’s

computer that uses ASCOM to command the

user’s telescope.

Declination Guiding - A Bigger

Challenge

As LX200GPS users are all too aware, the

LX200GPS exhibits significant backlash and

retrograde motion in the declination drive. While

this is a mechanical problem that cannot be

resolved with software or firmware, the

significance of the problem can be reduced.

Meade has provided a method to quickly take up

the backlash when reversing declination motion

direction by making appropriate settings through

the telescope’s firmware. Although the backlash

can be somewhat annoying for visual use, the anti-

backlash feature makes it tolerable. As mentioned

above, firmware versions 2.0i did not apply the

anti-backlash feature during guiding in polar mode.

This, in conjunction with the retrograde motion

exhibited by most LX200 telescopes, made

declination guiding very difficult.

In firmware version 3.0d, the anti-backlash feature

is active during guiding. This means that, if guide

star drift correction requires a reversal of

declination slew direction, the backlash will be

taken up by the drive before the correcting slew is

performed (assuming declination backlash

correction is turned on). Unfortunately, the

retrograde motion is still present, so the star goes

through some wild gyrations before settling in the

new position - but at least the gyrations occur

quickly and the star can be successfully directed

back to the proper position.

The effect of declination backlash on autoguidng

can be minimized. Unlike RA tracking, the

declination axis is not moving while tracking a

target. Movements in declination should only be

required to account for inaccurate polar alignment.

The target may be deflected northward or

southward due to seeing, but attempts to chase the

seeing are futile. Declination corrections for

imperfect polar alignment should only be needed

in one direction. Therefore, the following

suggestions should help minimize or eliminate

declination direction changes:

1) After any motions have been made in

declination (e.g. to center a new target), guide the

LX200GPS in declination (either autoguiding or

manually) for several minutes before starting the

next exposure. This should be sufficient time for

the direction of declination drift to be established

and for the declination drive to take up backlash

from the last direction change.

2) Set the minimum adjustment large enough that

the autoguider does not try to chase the seeing.

The software should be issuing all northward or all

southward declination guiding movements. (You

can check this using PortMon software. Or, if you

are using GuideDog, carefully watch the direction

buttons at the lower left of the program window.

The buttons will blink when a corresponding

motion is commanded.) It is important to avoid

overshooting the desired position, thus requiring a

direction reversal.

3) If your autoguider software allows it, set the

declination to correct in one direction only, or set

the aggressiveness much lower for the direction

that is not needed to correct for imprecise polar

In GuideDog, Steve Barkes has made extensive use of the

ASCOM blind commands to make use of Meade’s

undocumented :Mgdnnnn# command for more accurate

guiding.of the LX200GPS.

Some users have suggested purposely misaligning the

telescope by a small amount in order to ensure a small

declination drift and avoid declination direction reversals. It

is important that the misalignment be very small, in order to

avoid field rotation.

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