• ALC (Automatic level control) and LEVEL are two 'pots' on the side of an Auto Iris lens.
• PEAK and AVERAGE (P+A) are the parameters for the ALC control.
• HIGH and LOW settings 'H+L' are available on the LEVEL control.

ALC:

• Any bright areas in the scene, such as sun reflection through windows, street lighting, and so on, can be controlled with this adjustment. PEAK and AVERAGE are the two options.
• When set to PEAK, bright parts in the scene are given more weight, resulting in less contrast in the surrounding region. The brilliant regions can now be viewed in more detail.
• When set to AVERAGE, the lens ignores bright spots, resulting in over-brightness or flare in these places while increasing the contrast of the surrounding area.

LEVEL:

• The only accurate technique to set the VIDEO LEVEL is to utilise an oscilloscope, which is not a possibility for most engineers.
• Using a service test monitor and a camera that has been set up appropriately to 1 volt peak to peak is a more practical option.
• Place the video output from this tested camera on the test monitor and adjust the contrast and brightness until the picture is to your liking. Make a note of the contrast and brightness parameters so you can return to them.
• Set up each camera by changing the ALC (as described above) and then the LEVEL to get a picture identical to the test camera's. (Make sure your test monitor is set to the positions you highlighted)

NB: The ALC adjustment on most zoom lenses is a speed control for the Iris motor and should be left in the middle setting. Because the amplifiers on Auto Iris lenses are sensitive, use a professional trimming tool to change the LEVEL and ALC instead of a screwdriver, which can cause minor voltages.

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