Sensor orientation in 3d space.

The Z axis controls the amount of back focus and when it is adjusted correctly in all four corners then there will be no tilt and when I say adjusted correctly that means the sensor is in the exact position in 3d space to interact with light cone emitting from the telescope.

Sensor position in the light cone compared to an ASTAP image inspector tilt chart.

With the sensor at the proper back focus the perimeter hfd numbers will be a bit larger than the center number.

Intrafocal

When the sensor starts getting too close to the telescope the perimeter hfd number get smaller than the center hfd number.

This image is just to show which numbers will get smaller when too close.

Extrafocal

With the sensor too far out the perimeter hfd numbers will be much larger than the center hfd number.

This image is just to show which numbers will get larger when too far out.