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Explanation of terms for iris setting
AGC (automatic
gain control)
White clip
AES (automatic
shutter control)
Iris adjustment
This starts tooperate when the light intensity is insufficient to deliver a full video signal
(1Vp-p). The greater the gain, the greater the signal noise in the picture. It is generally
activated between 0.8 and 1.0Vp-p.
Signal limitation at high image amplitudes. The white clip value generally lies between
1.1 and 1.2 Vp-p.
This automatically controls the shutter times, it starts when the light intensity becomes
stronger and the signal would otherwise be limited/over-regulated by the white clip
feature. Automatic shutter control is mainly applied for manual lenses.
If a camera is operated with controlled lenses, regardless of whether DC or AI, the AES
must be switched off. Problems arise if this is not done because both control systems
try to steer the volume of light for the camera. As the AES generally reacts faster, the
iris remains fully opened and the shutter resumes the control work, which produces
major drawbacks. As the iris is open, the depth of focus is very low. When shutter
times are short, this can cause a smear effect (bright, vertical stripes in light parts of
the picture).
The working point of the iris should always be above the AGC start and below that of
the white clip. This range is very small with some cameras, making it difficult to adjust
the lens. It is therefore advisable to switch off the AGC (if possible) when adjusting the
iris. Once the lens has been focussed, the AGC must be switched back on (only for
cameras which allow the AGC to be switched off).
In the case of DC lenses, the working point of the iris is adjusted at the camera's level
potentiometer (the AI amplifier is built into the camera).
In the case of AI lenses, the level potentiometer is located on the lens (the AI amplifier
is built into the lens)
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