Optimal Use of the CCD Camera
The S/N ratio at moderate and high light levels is the square root of the light intensity. To increase the S/N one should pump in (and collect) as much light as possible at the lowest gain (1X). Only at this gain (1X) one uses the full well-size of the CCD and this is the preferred mode of measurement for most bath-stained tissue, such as brain slices and cardiac preparations. The saturation at higher gains (>=3X) is probably amplifier saturation. If saturation occurs at 1X, try to use a higher frame rate (100Hz, unbinned). This will allow emptying the CCD wells faster, thus avoid saturation w/o losing light. One can temporally bin the data later to increase the S/N ratio. If saturation still occurs when using the highest frame rate, one will have to reduce the illumination. Higher gains should be used at dim light levels to better utilize the 14-bit digitization.
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