Nikon SB-900 - Manual (Page 108)

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Flash modes and functions
Flash shooting support functions
AF-Assist Illuminator
When the light is too dim for normal autofocus operation, the SB-900’s AF-Assist
illuminator enables you to perform autofocus photography.
The SB-900’s AF-Assist Illuminator supports the dynamic-area AF system.
You can set the SB-900’s AF-Assist Illuminator to activate or cancel in the custom
setting mode. (kC-23)
The AF-Assist Illuminator cannot be used with cameras not compatible with CLS
and COOLPIX cameras.
Notes on using the AF-Assist Illuminator
The AF-Assist Illuminator is available, if an AF lens is mounted and the camera’s
focus mode is set to S (Single Servo AF with focus priority), AF-A, or AF.
The effective shooting distance with the AF-Assist Illuminator is approx. 1 m to
10 m (3.3 to 33 ft.) from the center of the image with a 50mm f/1.8 lens. The
shooting distance varies depending on the lens in use.
With a D3 camera, for example:
Suitable lens focal length is between 17 mm and 135 mm. Focus areas for each
focal length, in which autofocusing is available, are as follows:
The AF-Assist illuminator will not light up, if the camera’s autofocus is locked or
the SB-900’s ready-light does not come on.
Refer to your camera user’s manual for more information.
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17 mm – 19 mm 20 mm – 105 mm 106 mm – 135 mm