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The format describes the size of the light sensitive area of a CMOS sensor or CCD sensor. Due to historical reasons the format's unit is inch ["]. Due to the same reason the format's value does not "directly" express the physical size of the light sensitive area.

This confusion originates from the old days of video cameras fitted with pickup tubes ("Vidicon"). Actually, their outer diameter was 1/2", 2/3" and 1". Logically, the light sensitive rectangle at the front side of the tube was smaller. The following table shows the relationship between the format and the real dimensions of the light sensitive area [mm]:

Format: 1/4" 1/3" 1/2" 2/3" 1"
Height: 2,4 3,6 4,8 6,6 9,6
Width: 3,2 4,8 6,4 8,8 12,8
Subject to change

Important: Some industrial cameras allow their resolution to be reduced by software. For instance, this is the case for the One4all cameras offered by The Imaging Source. A reduced resolution simultaneously leads to a reduced format, and this in turn, leads to a reduced focal length of the lens.

Lens selection

The format of a CMOS sensor or CCD sensor does not only affect the calculation of the focal length of a lens. The format of the lens and the sensor also have to fit each other.

At first glance it seems to be logical that both have to be identical. But actually, the format of the lens has to be larger than or equal to that of the sensor. In practice, it is preferable to use a lens with a larger format, since optical flaws mainly appear at its rim.

Important: In contrast to the format of the sensor, the format of the lens does not affect the calculation of the focal length. The article Lenses for industrial cameras describes the relationship between format and focal length in detail.