Hereafter, we describe a problem that may occur if conversion factor measurements is carried out just few time after having set FIERA online. This has an effect to the QE measurement if they are made just after online because it takes time to get the data and the conversion factor is measured at the beginning of the process. Also during observation calibration the radiometric response may shift according to time after having set FIERA online. To avoid this issue, it is recommended to set online FIERA half of an hour before performing any observation or measurements. We think this phenomena behaves the same at least for all EEV CCDs.

EEV 44-82
CCD name : Annie
Serial number : 8171-4-1
Type : Backside, Single layer AR Pixel size 15x15 µm
Number of photosensitive pixels 2048 x 4102 [HxV]
Number of outputs : 2
Overall rating : Science

Conversion factor (e-/ADU) according to time, after having set FIERA Online.

QE calculation error due to conversion factor variation.

Here is a small example of mistake due to a conversion factor variation phenomena. The conversion factor is calculated at the beginning of the measurement and decrease after few minutes, and the consequence is a variation in the measurement. The red curve is unfortunately to much optimistic.

In general, the QE calculation on the test bench is the last one to be made. So this phenomena may not have an effect on the measurement.