Charge transfer efficiency problems with the camera

Many of the observations undertaken using L3Vision detectors at the NOT were affected by charge transfer efficiency problems in the detector (Tubbs et al. , 2002). This problem occurs if photo-electrons in the image and store areas of the CCD do not always move to an adjacent pixel when they are supposed to (i.e. if there is a small probability that any given electron will be left behind in a transfer). Electrons which are left behind in one or more of the transfers on the CCD are registered as if they had come from a different pixel in the imaging array, causing images taken with the CCD to be shifted in position and image scale, and to appear blurred.

The problems with charge transfer efficiency were found to vary strongly with the voltage settings in the camera and other environmental effects. I will briefly discuss the effect of poor charge transfer efficiency on laboratory measurements before analysing any of the data taken at the telescope. The charge transfer efficiency was found to be substantially better in recent experiments using the CCD87 than had been found with the CCD65, but there has not been time to include a quantitive assessment of these results here.