Meade RCX400 Bedienungsanleitung PDF herunterladen (Seite 5)

4. Default Position. In this mode, before each shutdown the telescope is set at a ﬁxed position

which coordinates are pre-installed with the command :hS# as default. Thus, when you turn the

telescope on, it already has the correct horizontal coordinate system. To work in the equatorial

system the exact time is needed. The disadvantages are obvious: turning oﬀ the telescope in the

wrong position or a random shifting in the oﬀ state lead to loss of orientation.

The Home Position is the only method that ensures the recovery of the coordinate system,

although its accuracy is not high. Another advantage of this method is its autonomy, it doesn’t

require periodic inspection of the telescope and remote manipulation. Therefore, this method was

used for 1.5 years as basic. However, after the failure of the level sensor (due to movements in altitude

the cable connecting the level/magnetometer board with the main board was broken), we had to look

for an alternative method of orientation recovery.

It turned out that the telescope can be set to the desired starting position with an accuracy of

better than 20 − 30

′

manually (by oﬀset commands) relying on image from the dome camera. Then

the telescope shutdowns. After subsequent start, the coordinate system will be consistent with the

telescope position. This procedure is so simple and reliable, that we use it for the last few months.

Reﬁnement of the coordinate system is called each time after a successful pointing on the measured

stars with help of the sync command :CA#. When work ﬁnished, the telescope is installed in the more

accurate starting position.

Another useful tool is a laser pointer, ﬁxed on the telescope tube and indicating the right initial

position with help of label placed on the enclosure wall. Positioning accuracy is better than 10

′

. Also

the return telescope to working position manually becomes simplier.

In principle, having the camera ﬁnder and using undocumented commands :EK...# (See next

section), one can perform the procedure Auto Alignment but we did not test this possibility.

4 Focusing and collimating

In principle the design of the focusing mechanism of telescope is a very progressive and ﬂexible.

However, the real implementation leads to the fact that in the process of refocusing telescope optical

system is gradually coming to unadjusted state: the corrector plate (with the secondary mirror ﬁxed

on it) become tilted. So-called secondary coma is appeared persistent throughout the ﬁeld of view.

In addition the optical axes of the instrument and the ﬁnder diverge. Extra focal image is not kept

as axisymmetric. Since the DIMM device uses two oﬀ-axis entrance aperture, this coma is seen as

astigmatism in both images.

Established electronics allows to collimate the telescope, i.e. to tilt the corrector plate in two

directions in such a way that the optical axes of the mirrors coincide. This procedure requires the

presence of an observer and it is not trivial task to execute it remotely even if you can see the image

in the ﬁeld of view.

However, if you use a single device as detector, you should inspect extra focal image without

violating working focus position. De-focusing of the image can be reached either by de-focusing viewer,

or by displacement of CCD camera. You must then carry out a thorough adjustment (collimation) and

remember it by the command “Collimation/Set Default” of AutostarII menu. Then the restoration of

the optimal collimation in optimal focusing position may be done with command “Collimation/Restore

Default”.

To remotely call the execution of the menu item “Collimation/Restore Default”, not having the

appropriate command in the list of remote commands, you can use an undocumented command

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