Equinox Systems GEMINI Manuel d'utilisateur télécharger pdf (Page 24)

Gemini Users Manual 19

Type. If you alter either the Mount Type or hemisphere, restart the Gemini after

completing the Setup operation. Simply turn Gemini off and then on again to do this.

IMPORTANT: The default safety limits prevent the mount from hitting itself as it

moves. However, these safety limits may not be sufficient to prevent your OTA from

hitting either parts of the mount or the tripod. You should always check the safety limits

and reset them as appropriate for your specific equipment. Please see section 5.3.10.2.6

for information about setting the safety limits.

2.4.3 Refining the Mount's Alignment Model

Let’s review where you are at this point: You have assembled the mount and telescope,

and have carefully balanced them in both RA and Dec. You have leveled and roughly

polar aligned the mount by pointing the mount’s polar axis at the celestial pole. You

have positioned the mount in the Startup Position with the counterweight down and the

telescope pointing north (or south if in the southern hemisphere), and powered Gemini

on. Finally, you used Gemini’s menus to set the various parameters to make it work.

You are now ready to align Gemini’s internal modeling parameters.

In order to improve the accuracy pointing to objects in the sky, the Gemini software can

learn how the mount is oriented with respect to the celestial pole, what angle the

telescope is pointing to in both RA and Dec., the degree of non-orthogonality between the

telescope and the mount, etc. All of these parameters form Gemini’s “model” of the

mount and telescope. These parameters as well as others are built up automatically

through a series of alignment operations. Each alignment consists of pointing to a star

and telling Gemini when that star is centered. Accurate modeling allows accurate GoTo

operations, and the more alignments you perform (up to a point), the better the modeling

parameters can be determined. You can read more about the various modeling

parameters that Gemini uses in chapter 3.

As mentioned earlier, there are several modes in which Gemini can start up. For the

purposes of this section, we will assume that the mount was “Cold Started.” Subsequent

sections of the manual will explain the modeling and alignment process in greater detail

for each of the 3 startup modes.

2.4.3.1 Choosing Alignment Stars

Unless you are perfectly polar aligned and have no mechanical play or misalignment in

your mount and your telescope, you will need at least 3 star alignments in order to build

an accurate model. These must all be on the same side of the meridian – either east or

west. The first 3 alignment stars should be selected from Gemini's "Bright Stars" catalog

(database) and must differ in hour angle (distance in RA from the meridian) by at least

one or two hours. This means you either need to choose stars that differ in RA by at least

a couple hours, or wait a couple hours between alignments so that your next alignment

star will differ in hour angle from where your first alignment star was. For example,

doing an alignment on Capella and then on Rigel or Bellatrix is not a good idea; the same

is true for alignments on Procyon, followed by Castor or Pollux – there are only tiny

differences in RA between them.

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Equinox Systems GEMINI Manuel d'utilisateur Page 24