Nauticam makes an optical trigger that sits on the hotshot and just fires the flash straight ahead. Since it doesn't have little LEDs that connect right to the optical bulkheads, you need to use the prism to redirect that straight ahead light, upward. The prism reflects the light up into the bulkheads. If you use a trigger that has the little LEDS you need to remove the prism and put the LEDs directly into the bulkheads. I have a Nauticam housing, but I'm using the UWTechnics TTL trigger so I removed the prism.
If you download the user's manual here, it will tell you about removing the prism http://uwtechnics.co...housings-detail
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