This master "flat frame" was created by combining (averaging) 30 individual 30 second images with the telescope and CCD camera pointed at a electroluminescent panel. The panel creates an evenly illuminated target, and the image provides a baseline of the imperfections in the telescope optical path-- this includes dust on the telscope optics (dust donuts) and vignetting by the CCD camera. The length of the exposure is determined by measuring the overall brightness of the image, with the goal of being approximately 1/2 of the CCD camera's saturation limit. During the creation of the master flat frame, the individual flat images are processed by subtracting a master bias frame. The master flat is applied to the raw images after a master bias frame has been mathmaticaly subtracted. Essentially this data is "divided" into the raw image.