Using The Flash:
The Coolpix has a built-in flash, which will illuminate nearby underwater subjects. For subjects that are farther away, an accessory slave flash is recommended. (See Below.) A built-in flash diffuser is supplied which will help achieve a wider and softer light source thereby providing more coverage and less likelihood of backscatter (the unattractive snowstorm affect of the flash reflecting off the suspended particles in the water). Further reduction of backscatter can be achieved by using an accessory off-camera slave flash. This will be discussed in more detail.
The need for artificial light to maximize color reproduction is necessary in nearly all pictures. Therefore it is strongly recommended that you set the flash mode to Flash Always. This will insure the flash fires on every exposure regardless of the ambient light conditions. (Please refer to the camera s instruction manual for more details.) Outdoor photographers do not have this same concern. There is no backscatter to be concerned with, and due to the ability of the flash to travel farther and more effectively in air as compared to in water, there is normally not a need for an accessory flash to provide proper illumination for most subjects.
Accessory Slave flash:
If you should use the Coolpix built-in flash as the master, you can trigger a second slave flash to provide more artificial light when needed. To do this, you must use an accessory flash that has a slave feature built in. The flash from the Coolpix must be aimed or bounced toward the accessory flash's slave sensor, or other fiber optic sensor. This will trigger the slave to fire in sync with the master flash. When using an accessory slave flash with fiber optic cable, it is recommended to black out the internal camera flash. The internal flash is located near the camera lens and can contribute to backscatter by illuminating floating particles close to the lens port.. If the sensor of the fiber optic cable is attached to the outside of the housing directly above the internal flash and taped over with black tape it will block out the light from the internal flash but transmit the light pulse to the external slave flash.