To properly process an astrophoto the first step in most cases is ‘calibration’. The purpose of calibration is to compensate for various defects in the image sensor and the optical system. Essentially, we capture images that isolate the most common defects and mathematically apply the inverse of the error to each of the raw images we have captured. One part of this calibration is to remove unevenness in the brightness across the frame. This step is called ‘flat calibration’. Unevenness (lack of flatness) can be caused by vignetting of light by the optical system (the image is darker in the […]