Hello Everyone,

Ever since I have been using CCDAP3 it has been subtracting 0.21 degrees from the target rotation on my RCOS Pir. If TheSky says 180 degrees CCDAP3 tells the rotator to go to 179.79. However, when taking flats CCDAP3 sets the rotator to exactly what is requested in the P.A. field on the flat setup screen. I searched the registry and found that the item Roffset is set to 0.210189117290797. How does this value get set?

To get flats using the offset I have been first taking a short exposure at the desired rotation. Then on the flat setup screen I leave the PA field blank.

Thanks,
Bob Franke
http://bf-astro.com

Hi Bob,

The rotator offset is determined by a plate solve position angle (PA) and the rotator position, factoring in the side of the meridian (SOM). This happens during the initialization process.

When taking flats, let CCDAP handle the offsets for you. Simply enter the PA of the target with "E" or "W" to denote the SOM that matches your data. CCDAP will do the rest.