Examples of filter ghosts near the FPA centre (bottom row) and near a corner (top row), highlighting the large field dependence. The left column shows an 80 × 80 pixel (24″ × 24″) cutout along with the automatic detection of the shape (red dashed line). Also shown is the final model (cyan solid line) used for Q1 based on the detection values, and the radius derived based on the magnitude of the source star (see Sect. 5). The middle column shows the total radial profile of the filter ghost cutout, and the Gaussian fit used as an initial guess for the detection radius. In the right column we display the edge image created from the Canny filter and the automatic detection of the shape (red dashed line) based on an elliptical Hough transformation.