The CCD chip size is often given in an inch measure: 1/2" chip, 2/3" chip, etc. Counter intuitively this does not refer to the chip diagonal in inch but has historical reasons. It relates the field-of-view of the camera to that of former tube cameras. The diagonal of the 1/2" chip is 8 mm, approximately 1/3 inch. The aspect ratios of the chips differ:
The table lists that a latest generation 2/3" CCD chip is considerably smaller than the field of view of a microscope ocular. For example, its diagonal is half the size of the diameter of a FN 22 ocular. This has important consequences for a light intensity optimised illumination, especially in case of critical illumination such as used for fibre coupling. If the exit slit of the light fibre is focused to a specimen area corresponding to a 2/3" CCD instead of the entire ocular area, which is four times as large, the intensity per area gain is a factor of 4.
The graphics show how the fields of view of a FN 22 ocular (top) and a 2/3" CCD chip (bottom) differ and how optimised critical illumination enhances on-chip brightness.
