... ARC 3.5m | ... 2.1 Choosing and Exposure Time . 2.2 Choosing the CCD Gain . ... 3.2 Read Times and Read Noise . ... At the slow read rate of 100 KHz to be used for exposure times longer than a few seconds, we determine an average read noise of order 3.7 ? ... Table 2: Exposure time must be greater than the readout time by at least 0.03 s. The Agile CCD camera has two readout amplifiers, one of which is capable of reading at the fast readrate of 1MHz while introducing a read noise of order 7 ? ...