Flat field calculated using Chae’s method. It is based on 115 lunar images ‘dithered’ randomly around a central point. The dust speks near the middle are recognized from conventional FFs. The two diagonal stripes are also recognized as part of this CCDs extraordinarily strong fixed-pattern. The gradient from blue to pink and white corresponds to 2%. The image is based on B-band images from the night JD2455847.
It turns out that ‘slopes’ in this method has to do with the normalization of the source intensity – the method depends on the source being constant, but the source is not constant if it is partially on the dge of the image frame, is it? We are working on this.
