Meade LX200 CLASSIC Bedienungsanleitung PDF herunterladen (Seite 5)

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Apparently, Meade has added the command

:Mgdnnnn# to the MTSCP and didn’t tell anyone

about it. This command instructs the telescope to

move in direction d at the current guiding rate for

nnnn milliseconds. It is the perfect command for

autoguiding because it does not require a follow-

up command to halt the movement, and therefore

does not rely on the timing of commands issued

over the RS-232 interface.

This second point is important. While personal

computers have highly accurate timing, this does

not mean that they have the ability to issue signals

over the COM ports at precise times. This is

because the COM port traffic timing is affected by

system interrupts. For one reason or another, the

system resources needed to handle COM port

traffic may not be available at the precise time that

the software wishes to send it. When this occurs,

the signal may be delayed until the resources are

available. As a consequence, the interval between

a :Md# and a :Qd# command may be shorter than

expected (if the :Md# command was delayed) or

longer (if the :Qd# command was delayed). The

:Mgdnnnn# command solves this problem by

providing both the slew direction and duration

information in a single command. It is left to the

timing of the LX200GPS processor to accurately

implement the command. Presumably, this is a

much more accurate method.

Steve Barkes has already implemented :Mgdnnnn#

into GuideDog version 1.0.6. Peter Katreniak and

Axel Canicio have released beta testing versions of

K3CCDTools2 and Astrosnap Pro (respectively)

using the :Mgdnnnn# command.

Two Problems Solved by Meade, But....

In early October 2004, Meade released firmware

version 3.0d for the LX200GPS. In this version,

Meade has finally eliminated the 200-500

millisecond tracking pause following slew

commands. This important correction means that

guiding using the :Md# and :Qd# commands can

be expected to work, at least to some degree.

In firmware version 3.0d, Meade also solved

another important problem related to guiding.

Firmware version 2.0i, unfortunately, did not apply

the anti-backlash feature during guiding. This, in

conjunction with the retrograde motion exhibited

by most LX200 telescopes, made declination

guiding very difficult.

As usual, though, when Meade giveth with one

hand, they take away with the other. In version

3.0i, it is not possible to reload the user’s Periodic

Error Correction tables to the LX200GPS using

the Autostar Updater utility.

This means that, if a

user clears or overwrites a good PEC curve, there

is no way to restore the previous data. Hopefully,

the next firmware version will correct this, without

removing another important feature.

ASCOM

The Astronomy Common Objects Model is a set

of standards for scriptable/programmable low-

level control of astronomical instruments and

related devices. In practical terms, ASCOM acts

like a universal driver set for astronomy software

to use to communicate with ASCOM-compliant

telescopes, observatories, etc. In order to achieve

this, ASCOM must include telescope-specific

drivers. The ASCOM platform includes several

drivers that are potentially relevant to LX200GPS

telescopes. The driver most closely matching the

LX200GPS is Meade.Telescope, which is selected

in the ASCOM dialog as “Meade LX200 and

Autostar.”

Just like any other software, however, the ASCOM

platform must use the MTSCP to command the

LX200GPS. The version of the ASCOM platform

that is current as of this writing (version 3.03) uses

the :Md# and :Qd# commands for guiding

movements; it does not use :Mgdnnnn:. In testing

I have done with the ASCOM platform, I found

that many of the commands included in the

ASCOM specification do not work properly with

the LX200GPS. ASCOM is still in its infancy.

There is an ongoing attempt to develop drivers for

many telescope and mount types simultaneously,

so errors and omissions are to be expected.

Fortunately, the ASCOM platform includes a

“blind command” function, which passes a

command string literally and without interpretation

Although PEC tables may not be uploaded using the

Autostar Updater, Dick Seymour reports that Andrew

Johansen's PEC Editor has already overcome that

obstacle. See the references section for a link to download

Andrew’s program..

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