Dark Current Measurement Technique

1) Acquire a dark image. There should be no stray light hitting the CCD. A three to five minute dark exposure is sufficient for good statistics.

2) Measure camera gain. This requires generating a Photon Transfer Curve. Refer to the User Manual.

3) Measure the average pixel value for the dark image. For multi-port CCDs, measure each sector in the image separately.

4) Measure the average pixel value for the bias strip in the image. For multi-port CCDs, measure the bias for each sector in the image.

5) Subtract the average bias value from the average dark value. For multi-port CCDs be sure to calculate each image sector separately. Divide this value by exposure time. This is the dark current in ADU/pixel/second.

6) Multiply the dark current in ADUs by the camera gain (measured in Step 2) to convert to electrons/pixel/second.

7) Note that dark current is approximately cut in half for every 6 o C reduction in operating temperature. Dark noise follows Poisson statistics and is equal to the square root of the dark current. Dark current can be subtracted from the image whereas dark noise cannot.