ARRI 535B - Manual (Page 32)

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5.2 Mechanical Iris
Only a relatively small portion of the light which passes
through the film camera´s lens goes to the CCD chip of the
video assist, as the light is shared between the viewfinder,
the CCD chip and the film. Therefore the IVS lenses are
designed for normal usage with a totally open iris to have
maximum light on the CCD chip. Variations in lighting
are compensated by the IVS gain control (automatically
or manually).
Under certain conditions, such as when lighting is set for
low sensitivity film (under 100 ASA) or for motion effects,
it is possible that the IVS gain range is exceeded. In this
case the mechanical iris of the IVS lens can be closed.
Check all settings on the connected monitor.
If the mechanical iris is closed more than necessary,
the IVS will compensate by increasing the gain
and improve the image brightness electronically.
This creates additional electronic noise.
To avoid this, always open the mechanical iris
as far as possible.
mechanical iris
Standard Video Controls