Equinox Systems GEMINI Manuel d'utilisateur télécharger pdf (Page 41)

Gemini Users Manual 36

button to slew back and forth between the two stars. When you are finished, press the

MENU button once more, and when the telescope starts to slew, press the RA+ button to

escape from the loop and finish the polar alignment routine. You can expect to get to

within one degree of the pole using this method.

IMPORTANT: Because this method depends on the mount pointing to where the stars

should be if the mount were polar aligned, you cannot use this function if modeling

parameters have already been calculated. You should only use it after a Cold Start before

you do any Additional Aligns, or immediately after selecting the “Reset Alignment”

menu item.

Polar Axis Correction

This feature assists you in accurately polar aligning your mount. Because Gemini's

modeling feature calculates the mount's deviation from perfect polar alignment, it can be

used to guide you to alignment as you adjust the mount's azimuth and elevation. It is

important to note that before you can use this function, you must build an accurate

pointing model by doing several Additional Aligns.

After you have done several alignments on different objects, select an object from the

Object Database that is near the intersection of the celestial equator and the meridian.

GoTo the object and center it in the eyepiece using the HC buttons. Now, select "Align

Telescope→Polar Axis Corr." from the menu. Gemini will move the mount to where the

object should be if the mount were accurately polar aligned. You should adjust the polar

alignment of the mount using the azimuth and elevation adjustment knobs until the object

is again centered in the eyepiece. Since the mount will approximate perfect polar

alignment, all subsequent GoTo operations should result in target objects being near the

center of the eyepiece. If not (for instance, because the mount's initial misalignment

exceeded several degrees), you may repeat the correction process. Note that after using

this function, the modeling parameters will be reset and you will need to rebuild the

model by performing several alignments on different objects. If you are within about 2

degrees of being polar aligned and have done at least 5 Additional Aligns, you can expect

this function to get you within 2 arc minutes of precise polar alignment.

3.4.3 Accuracy Required

How well must Gemini be polar aligned? The answer to this question really depends on

what you are doing. For visual observing, it does not need to be well aligned at all. You

can be as much as 6° off, and the modeling parameters will still allow accurate GoTo

performance. In addition, you can use Closed Loop tracking to keep objects centered

while observing.

Imaging requires more accurate polar alignment due to the possibility of image rotation.

While Gemini can GoTo and track objects when polar alignment is off, the field of view

in the telescope will slowly rotate as tracking takes place. The closer the mount is to

being polar aligned, the less field rotation will occur. Field rotation is a problem

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Equinox Systems GEMINI Manuel d'utilisateur Page 41