Equinox Systems GEMINI Uživatelský manuál stáhnout pdf (Strana 51)

Gemini Users Manual 46

The following table lists the number of steps per second (sidereal tracking) for several

mounts:

Worm Period Steps per second

239.344658 sec. (G-11, HGM-200, MI-

250)

26.73967759

319.1262611 sec. (HGM Titan) 20.05475819

478.68939 sec. (GM-8, CI-700) 13.3698388

319.1262611 sec. (Titan 50) 40.10951639

4.3.2.5 Drift Correction

When you train the PEC, it is assumed that the only error being corrected is the periodic

error in the worm. Because of the periodic nature of this error, the star will appear to

drift back and forth in RA during the period of the worm's rotation, but will always end

up in the same spot at the end of every rotation. Theoretically then, at the end of a

training run, the total amount of correction to the west should exactly equal the total

amount of correction to the east. If, however, there was systematic drift of the object

caused by something other than periodic error (i.e. misalignment of the mount,

differential refraction, etc.), then the corrections made during the training run would

reflect this error also.

This is not a problem if (1) the object being imaged is the same as (or very near) the

object used to train the PEC and (2) the mount has not been moved since the training. In

that case, the same systematic errors that were present during the training run will also be

present during playback, and both the periodic and systematic errors will have been

corrected. However, in many cases, you will want to use the same PEC data for widely

scattered objects over several observing sessions when the telescope has likely been

moved between the sessions. In this case, the amount of systematic error will likely be

different than during the training run, so just playing back the corrections made during

training will actually introduce errors.

Drift Correction solves this problem by effectively removing the systematic drift

component from the recorded PEC data. If everything were perfect and there were no

systematic drift, corrections in both directions would cancel each other out, and this

feature would not be needed. If, however, they do not cancel out after a worm period, the

existence of systematic drift is assumed.

Selecting this menu item removes this non-periodic component. Gemini sums up the

corrections (negative and positive) made in both directions, and spreads them evenly

throughout the worm period. It does not, however, change the tracking rate itself, because

to do so would lead to imprecise tracking in other regions of the sky.

Because you may choose to train the PEC on the same object as the one that is to be

imaged, Drift Correction of the PEC data is not done automatically after each training

run; this helps minimize the guiding corrections necessary. You should only select the

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Equinox Systems GEMINI Uživatelský manuál Strana 51