There are consistent problems that occur during the process of capturing astronomical images which cause defects to be present on the raw image captured. Some of these problems include vignetting, dust on the lens or the digital sensor’s surface, and dead or less sensitive pixels. This is a problem when the images are meant to be used in photometry, where the brightness of each pixel is taken into account. One can simply clean all surfaces of dust, but it will always come back. A more solid solution is to use a calibration frame called a “flat field” to correct each image before processing it. This “flat field” is created by pointing a telescope at an area characterized by uniform luminosity and color— white is preferred— then capturing an image. The only things visible in these calibration images will be the anomalies previously mentioned, and that’s the flat field: a portrait of the dust and shadows seen by the camera. After the astronomical image is captured, the flat fields are averaged and then divided out of the astronomical image. All that is left then is what was captured from the cosmos, rather than what was on the lens or sensor. The purpose of this project is to create a flat field box that could be used to calibrate the 20-inch telescope in USU’s observatory. This box will be fitted with two panels of translucent opal plexiglass and a panel of evenly spaced miniature incandescent light bulbs. The bulbs will illuminate the acrylic sheets from behind and the telescope will have a view of a uniform “flat field.” This calibration instrument will allow the telescope to be used for photometric purposes and other areas of astronomy.
Bunn, Catharine, "Constructing a Flat Field for Scientific Astronomical Imaging" (2014). Physics Capstone Project. Paper 10.