7.6 Linearity of CCD
93
Fig. 7.8 Example of the DS9 region layout for the flat field practical
7.6 Linearity of CCD
Unlike photographic film, which does not respond in a linear manner when exposed
to light, the response of a CCD is linear over most of its dynamic range (around
1000–65,000 counts for 16-bit cameras). Hence, doubling the exposure time doubles
the count in an exposed pixel. However, when the counts begin to get high, such as
with very long exposures or very bright objects, CCDs tend to become progressively
nonlinear before becoming saturated and no longer responsive.
It is important to determine where this point for nonlinearity lies so it can be
avoided. This is normally determined using a modified version of the flat field technique outlined in Practical 2.
93
Fig. 7.8 Example of the DS9 region layout for the flat field practical
7.6 Linearity of CCD
Unlike photographic film, which does not respond in a linear manner when exposed
to light, the response of a CCD is linear over most of its dynamic range (around
1000–65,000 counts for 16-bit cameras). Hence, doubling the exposure time doubles
the count in an exposed pixel. However, when the counts begin to get high, such as
with very long exposures or very bright objects, CCDs tend to become progressively
nonlinear before becoming saturated and no longer responsive.
It is important to determine where this point for nonlinearity lies so it can be
avoided. This is normally determined using a modified version of the flat field technique outlined in Practical 2.