Photometry preparation in the Focus module
In order to process automated reliable photometry measurements, Ekos needs to capture precisely comparable star profiles. This means focusing on specific targets, and readjusting focus to obtain a precise FWHM on those specific targets.
For instance, measuring Cepheid luminosity requires precise control of the apparent profile of a nearby reference star to be able to plot variations reliably. Indeed, another famous application is measuring exoplanet transits.
Focus therefore requires two improvements:
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Ability to focus on a catalog object. This requires obtaining the object coordinates, then plate-solving focus frames to locate and use said object as focus source.
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Ability to de-focus to a specific HFR or FHWM value, in a specific mechanical direction, after achieving optimal focus on the catalog object.
The Focus procedure should retry then report failure if the catalog object coordinates are out of the captured frame extents. The Align module should be used first instead.
It is often desirable to capture the reference and measured stars together on the same frame for visual verification. If that is not possible, due to the dimensions of the field of view of the optical setup, or more simply to retain the same reference for multiple measurements, the Scheduler will offer enough flexibility to first slew to and focus on the reference object, then slew to and capture the measured object without altering the focus.
It may also be interesting for Focus to revert the mechanical position to the last optimal focus position before running a focus procedure again, in case the de-focus adjustment causes a large offset that prevents the next procedure from succeeding. If implemented, reverting to the optimal position should only happen in a fully automated procedure: as soon as the end-user changes the position of the focuser manually, that optimal position should be forgotten.