Meade Image Processing Manuel d'utilisateur télécharger pdf (Page 18)

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● The imaging hardware

There is one 12-inch Meade Schmidt-

Cassegrain telescope (with a built-in focal

reducer f = 1800 mm, f/5.9) reserved for work

with the CCD (see Fig. 9). This telescope is

acceptable optical quality, and it is mounted

on a state-of-the-art quality permanent

equatorial mount on the pier in the little dome

of Kennon Observatory. A great advantage of

using a permanent setup for the telescope is

that the right ascension axis is very carefully

aligned with the North Pole. The telescope

will track the stars much more precisely than a

telescope on a tripod. In addition, the shaking

from people walking around and from wind

gusts is reduced.

The standard setup is shown in Figs. 9-10.

The elements added to the telescope are a

focuser, a filter wheel, and the camera.

(i) The focuser can move the camera

assembly in and out. It is crucial to

have the chip in the exactly correct

position (focusing), preferably with a

precision of

±

0.05 mm. (Each 0.01 mm

of defocus makes stars into a blur of

diameter 0.2 as, cf. pixel size 0.78 as)

The telescope’s original focuser is too

crude for such precise focusing. The

focuser has a built-in electric motor to

move the assembly. A hand control’s +

and – buttons move it in or out, and the

position is indicated on a screen with the

precision of

±

0.01 mm. The focuser can

move the assembly a total of 13.00 mm.

(ii) The CFW10 filter wheel (see Fig. 3)

contains color filters. In order to take

color images, we need separate ones in

each of three colors (RGB – red, green,

and blue) and compose the final color

picture by computer.

Fig. 10: The camera head.

Fig. 9: The 12-inch Meade telescope.

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