Celestron Compustar Manuál s instrukcemi stáhnout pdf (Strana 5)

What Is Guiding?

Because of these tracking errors, virtually all astrophotographs must be guided. That is, the

tracking of the drive and mount are monitored in both the east-west and north-south direction

throughout the exposure and all tracking errors are promptly corrected. Traditionally, this has

been done manually by the astrophotographer using a device known as a drive corrector. Drive

correctors typically have hand controllers with four directional buttons, one each for north, south,

east and west corrections. When one of these buttons is pushed, electronic switches activate drive

motors to move the mount by a small amount in the corresponding direction, thus correcting a

tracking error. In the case of the subject drifting too far south, pushing the north button on the

hand controller activates the drive motor on the declination axis to move the mount northward.

The east and west buttons affect the clock drive motor on the right ascension axis, moving the

telescope east or west, as required.

During the exposure, the astrophotographer cannot actually see the subject being imaged by the

camera. To guide, the astrophotographer has to monitor a star, known as a guide star, being

tracked by the same telescope drive and mount as the camera. The goal is to detect tracking

errors and correct them before they would cause noticeable trailing on the final image. To do

this, the astrophotographer has to have some frame of reference around the guide star. This is

provided by a guiding eyepiece, also known as a guiding reticle. The guiding reticle projects an

illuminated red cross-hair into the field of view of the eyepiece (Figure 1). The guide star is

centered on the cross-hair which makes guiding errors, and their direction, immediately apparent.

The astrophotographer has to remain at the telescope, essentially playing a simple “video game”-

-if the star drifts north, move it south, if it drifts west, move it east, and so on,-- for the entire

duration of the exposure(s), which might be hours. Staring at a guide star, being essentially

motionless for these long periods of time, one can get very cold (normally, much of one‟s body

heat comes from muscle movement) and mentally fatigued and this can easily lead to guiding

errors that may degrade the image.

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Celestron Compustar Manuál s instrukcemi Strana 5