The amount of light is changed by controlling the flash duration, and this is usually referred to as the intensity. The flash tube takes time to reach maximum output, and then its light diminishes. Stopping anywhere in this time period is how the amount of light is controlled.

Duplicating the time duration of a pre-flash may not produce the same amount of light because different strobes takes different times to reach their peak intensity. The exposure of many digital cameras is dictated by measuring the pre-flash, so its intensity is important.

Varying the pre-flash intensity will control the amount of light the camera dictates for the main flash. The pre-flash switch of the wireless TTL Sensor presets different intensity levels.

Setting the camera to a lower ISO range of 64 or 100 tells the camera that more flash will be required for proper exposure. Similarly, a smaller aperture (i.e. bigger number like f/8) will dictate more flash than a large f/2 or f2/8 aperture setting.

Many digital cameras utilize a pre-flash with a duration that is too short for the powerful underwater strobes to duplicate. If the pre flash of an underwater strobe is too different, the camera may not provide proper exposure.

The SubStrobe Manual Controller provides consistent results with these cameras without requiring fibre optic "sync cord" nonsense. Simply aim the Controller at the housing for dependable strobe triggering.

Digital SLR cameras do NOT operate TTL with any current underwater strobes unless conversion circuitry is included in the housing. Ikelite has conversion circuitry to provide TTL for many Canon, Nikon and Olympus models.

Surface strobes in a housing will not provide the wide angle coverage of an underwater strobe. The cost of a strobe housing usually approaches that of a complete underwater strobe with its faster recycle time, more power and better coverage.