Test of Engineering model s/n : 00352-02-02

3.2.1    Flat Field

A flat field was obtained by using a light emitting diode with a diffusing screen placed between the diode and the CCD. As these measurements were made at room temperature a dark signal measurement was also taken, and this has been subtracted from the original flat field measurement to produce the flat field shown below (figure one).

Figure one, the flat field taken at room temperature, with the data scaled between a minimum of 0 and a maximum value of 256. The image quality appears to be good, with only one column defect visible.

Figure two below shows the same flat field image but without any scaling of the data.

Figure three shows a histogram of the data accross row 100.

There is much more variation in this flat field than for the first engineering model CCD, although the flat fielding setup is the same. More investigation is required to see whether this variation is inherent to the CCD.

The mean value of the image is 1094 counts with a sigma of 34.

 A clearer picture of the uniformity (or otherwise) of the flat field can be found if all values above and below 3 standard deviations are scaled to either 0 or 256 respectively. The cosmetic blemishes are still present (as the values of these
blemishes have simply been re-scaled rather than removed). Figure four shows the new image obtained.

Finally, all pixels which have values greater or less than three times the standard deviation have been replaced by the mean value.

3.3.2 Full well

The figure below shows the variation in CCD output with increasing led on time.