ACP supports imager rotators via its observing plans. ACP Planner allows FOVI capture of rotation angle from both StarryNight and TheSky during its in-planetarium planning, as well as input of rotation angle on manual target entry. This rotation angle is included as part of the coordinates for each target in a plan.

For more details see the paper Rotated Guiding of Astronomical Telescopes (Acrobat).

During operation with a German mount, ACP automatically rolls the rotator over 180 degrees when the GEM flips, guaranteeing that the target orientation remains constant in acquired images and guaranteeing that the same guide star is used after the flip.

Post-Flip Recentering

Typically, a flip causes some small pointing error. On imagers with internal guiders having very small guide chips (original ST-7/8), it's possible for the guide star to be lost after a flip, even with accurate 180 degree roll-over. If ACP fails to start the guider after a flip, it will do a plate-solve and pointing update re slew, then try again to start the guider. In virtually all cases, this will automatically restore guider tracking on the originally selected guide star.

Auto-Calibration of Rotator

In contrast to other rotator support solutions, ACP automatically and dynamically compensates for any difference in alignment between the camera and the rotator. There is no need to do any math in your head for converting indicated rotator angle into sky PA. And if there is any slippage or change in indicated versus actual PA, ACP picks this up immediately (from its plate solution) and adjusts the bias between indicated and sky PA.

Always Sky Position Angle

ACP rotation angles are always equatorial or sky position angle (PA). This is true even on meridian flip. So if your target happens to be west of the meridian, where a GEM has flipped and the rotator rolled 180 degrees, the position angle of your acquired images remains constant. This makes it easy to stack images later, without having to roll over the ones acquired on the west.

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