KStars 3.6.8: Aberration inspector to analyse backfocus and sensor tilt

KStars/Ekos is updated every two months. Most updates include improvements, bug fixes and updated equipment support. But some updates introduce more fundamental new functionality. KStars 3.6.8, released early December 2023, is such an update. Introduced is an aberration inspector, not dissimilar to the one seen in N.I.N.A. The tool is the work of John Evans, who has greatly improved the autofocusing capabilities of KStars/Ekos in recent years.

The aberration inspector works as follows. After a regular autofocus routine, the software analyses the HFR values in each of nine panels in the image. From these values it calculates the deviation from optimum focus in each panel, both in focuser steps and µm. Those numbers are then interpreted in terms of sensor tilt and backfocus deviation. Besides a numerical result, there is also an intuitive graphical representation of both the sensor plane and the petzval surface (flatness of the image from the flattener),

Based on the information presented, you can start changing the backfocus distance, or if you have a tilt adjuster, change the settings of the adjuster to eliminate tilt. Currently the amount of backfocus and tilt adjusting to apply will require a bit of trying out for your own setup. But in a future upgrade, more quantitative feedback will be given to make the necessary adjustments.

KStars/Ekos is free software and can be downloaded from the KDE website. For an explanation of the tool and instructions how to use it, John Evans has published a very informative video on YouTube. On John’s Youtube channel there are a lot more videos available on how to use autofocus in KStars/Ekos.