9.4 Linearity Test

We want to test, whether our CCD is linear, i.e. whether the level we read out (when bias has been subtracted, of course), N, is proportional to the integration time, t, times the intensity of the light reaching the CCD, I.

We envisioned that we could do two tests of the linearity of the CCD. An indirect test where we would test whether the conversion factor was constant with level, and a direct test where we would test whether the level per unit time was constant with level. Results from these two test are reported in Sect.  and below.

For both purposes, 68 dome flats were taken, with an attempted constant light source. 2 filters were used: Johnson B (JB) and Gunn r (GR). Only the section [1:1060,300:700] (in untrimmed coordinates) was read out (this should not affect the results). All the images were taken in pairs with equal exposure time. The exposure time was varied in on order to span the full range of the CCD (0 - 65535 ADU). In between every one or two pairs of exposures with varying exposure time, a pair of exposures with exposure time 10 sec was taken. The sequence of exposure times is shown in Table .

 

Table: Exposure Times for the 34 Pairs of Images used for the Linearity Test

Johnson B:	10, 1, 2, 10, 4, 7, 10, 15, 20, 10, 30, 45, 10, 60, 10, 80, 10, 100, 10, 120, 10
Gunn r:	10, 2, 4, 7, 10, 15, 20, 10, 30, 45, 10, 55, 10

 

Notes: The exposure times are in seconds. The images are dfsc2284-2325 (JB) and dfsc2327-2352 (GR).