I had never been satisfied with my sky flats taken at dusk or dawn. Prominent donuts remained which should have been removed with good master flat. The problem with sky flats is that the brightness changes rapidly and the exposure must change to the image to 2/3 or so of saturation. This means normalizing the background. With the Aurora flatfield panel the exposures are all the same length. The master flat works very nicely to give a uniform background and removal of donuts and gradients. And best of all, no need to rush to finish while the sun sets or rises. This is a very useful and effective tool for imagers.