An ND1 (Neutral Density) filter should be placed in front of the lens when setting the back focus of a Color camera for low light conditions. An ND3 (Neutral Density) filter should be placed in front of the lens when setting the back focus of a Mono camera for low light conditions.

In order to set the back focus of a Mono camera equipped with I/R illumination for low light circumstances, an IRP (Infra-Red Pass) filter should be placed in front of the lens.

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