Do you need to buy a focus light ? Focus lights aren't necessary in all situations but are highly recommended in your dive trip .As water absorbs light quickly ,using a focus light allows the camera to see the obejects and quickly focus .using a focus light is critical for shooting at night . it also serves as a primary dive light . for shooting supermacro and oftentimes for shooting macro . Digital cameras, both compact and DSLR, focus by detecting contrast at the focusing point. Many experienced photographers use focus lights while shooting wide angle into bright sunlight as well.
you can go dive without a focus light or hold a dive light in your hand or mount an inexpensive dive light on your camera lighting arm system . sometimes , we will use a video light as a focus light
Will I see the focus light in my images?
Because critters are usually shot at fast shutter speeds and small apertures, the light from a focus light often doesn't show up in a photo. One thing is for sure: you'll have a higher chance of getting a hot spot if you're shooting macro at f/2.8, 1/60th than if you're shooting at f/16, 1/250th. Small apertures and/or fast shutter speeds block out most of the ambient light, including your dive light, especially if you are using the edge of the beam. Strobes provide the light that illuminates your photo subject.