Focuser calibration
This function help you to set the auto-focus parameters specific to your focuser, telescope and camera because it is not immediately evident what to set for all this numbers.
The principle is you start by centering and manually focusing a star field that is used by the procedure to find how the stars diameter change with the position of the focuser.
At the end it propose you new auto-focus parameters you can save to the configuration.
To start the procedure select the menu Tools → Focuser calibration
In the first screen, set the exposure parameters that will also be used later when autofocusing.
Change the value for Step size. When the focuser position change by this value there must be a small change in the star diameter in the image. But be sure to not set it too large, it can be increased automatically later in the procedure.
When ready click the Start button.
It start by estimating the influence of the seeing condition to the star diameter.
Then it start moving the focuser, this can result in increasing or decreasing star diameter.
Anyway it will continue in the same direction until the diameter is increased by a significant amount.
Then it reverse the direction to search for the minimal diameter.
During this move back the two curve must ideally be superimposed. If not this is an indication you must change the Backlash setting in the Focus preference. Start by setting the backlash to two time the horizontal distance between the two lines at a given HFD.
The measurement continue after it found the minimum HFD position.
It stop after there is enough measurement, the focuser is moved to the minimum HFD position. After reviewing the curve click the Next button to show the result.
Review the parameters and click Save to record them in the configuration and exit the calibration tool.
Later you can view or change this values in the auto-focus parameters.
It is good to test this new parameters immediately by using the Autofocus button in the Focus tab.