Results

To test the gain measurement with two TDI images, sets of data from five CCDs are used. Based on the procedure developed above, the photon transfer curve for each CCD is plotted (see for example Fig. 3) and the conversion factor calculated. The results are in Table I. The gain measured with one (see Appendix B in this paper) and two TDI images are in accordance with the variance method (see Appendix A in this paper) used in the OmegaCAM test procedure. The maximum difference in this set is 1.5%. These results are very promising.

Figure 3. Example of a photon transfer curve realized with two TDI images.

The variance method used to measure the gain in the OmegaCAM procedure has been compared to the measurements of the gain made with the 55Fe method. The results show that both techniques are in accordance. Further confidence to the method is related to non linearity. When this defect is observed in the standard photon curve, the photon curve from TDI images shows the defect too.

Table 1. Gain measured for five CCDs with three different methods.

CCD serial number

Gain (e-/ADU) obtained from

One TDI Image

Two TDI Images

Variance method

02263-07-02

2.60 ± 0.01

2.58 ± 0.01

2.59 ± 0.02

02111-01-02

2.51 ± 0.01

2.50 ± 0.01

2.52 ± 0.02

00152-01-02

2.64 ± 0.01

2.62 ± 0.01

2.58 ± 0.01

02111-05-02

2.50 ± 0.01

2.50 ± 0.01

2.51 ± 0.01

02111-13-01

2.62 ± 0.01

2.60 ± 0.01

2.62 ± 0.01

In column one are the serial number of the CCDs. In column two is the gain measured with one TDI image. In column three is the gain from two TDI images and in column four, the gain measured with the photon transfer technique.

In column one are the serial number of the CCDs. In column two is the gain measured with one TDI image. In column three is the gain from two TDI images and in column four, the gain measured with the photon transfer technique.

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