![]() For this camera, the linearity limit is around 55,000 counts,Ĭorresponding to a dark current of roughly 82 $e^-$/sec. The dark current is also not well estimated for pixels a bit below the maximumīecause CCDs stop responding linearly once they pass a pixel value that depends The noise in the combined image is proportional to $1/\sqrt.įor the hottest pixels in this image, that is the lower limit of the dark Take several of these images and combine them to reduce the noise in the.That the expected dark counts is at least as large as the noise expected in a There are two ways to ensure that you are measuring dark current: If that isn't the case then theĭark images will be measuring noise, not dark current, as we saw in the Is larger than the expected noise in the image. Measuring the dark current in a camera requires taking images with fairly longĮxposure time, ideally long enough that the expected counts due to dark current Handling overscan and bias for dark framesĬombine calibrated dark images for use in later reduction stepsĬlick here to comment on this section on GitHub (opens in new tab). ![]() Real dark current: noise and other artifacts Non-uniform sensitivity in astronomical detectors The version here will remain online indefinitely but will not be updated. Please go here for the up-to-date and maintained version. This version of the CCD guide is out-of-date.
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