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Formula 16 Size of the Guiding Box
GB = T *15
Where:
- GB is the size of the Box in the Guiding eyepiece in arcseconds
- T Time in seconds it takes for a star on the celestial equator to drift across the box
- 15 is the number of arcseconds a star on the celestial equator drifts in one second
To measure the size of the guiding box by this formula, find a star on the celestial equator and meridian. Orient the cross hairs of the guiding eyepiece north-south and east-west. Put the star on one cross hair of the box with the guiding eyepiece in the guidescope. Turn the telescopes drive off, and time how long it takes for the star to drift across the box to the other cross hair. Repeat this procedure several times and average the results to get a more accurate reading.
Example:
It takes 2 seconds for a star on the celestial equator to drift across the guiding box with the telescope drive off. How big is the guiding box in arcseconds?
GB = T *15
GB = 2 *15
GB = 30
The size of the box in the guiding eyepiece is 30 arcseconds.
If you are shooting with a 5 inch f/8 scope and you can form 2.18 arc second stars, then your most critical guiding tolerance is going to be about 1/15 of the box diameter and your relaxed guiding tolerance is going to be about 1/8th of the box diameter.
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