As can be seen in the included screenshot (from an iTelescope-calibrated T33 H-alpha image of NGC 253) the corners of the image are bright, likely due to poor flat-fieldling or maybe some form of stray light or vignetting. Irrespective of the cause ApFindStars detects spurious stars. These in turn throw off Astrometry.net.
ApFindStars needs some way of ignoring these sources. These spurious sources dominate the brightest 200 star count, pushing out real stars, so ignoring them at the ApAstrometry stage is too late.
As can be seen in the included screenshot (from an iTelescope-calibrated T33 H-alpha image of NGC 253) the corners of the image are bright, likely due to poor flat-fieldling or maybe some form of stray light or vignetting. Irrespective of the cause
ApFindStarsdetects spurious stars. These in turn throw offAstrometry.net.ApFindStarsneeds some way of ignoring these sources. These spurious sources dominate the brightest 200 star count, pushing out real stars, so ignoring them at theApAstrometrystage is too late.