Light arm offset from the lens
A modular arm that puts the torch 25 cm out to the side, so the particles in the water do not light straight back into the camera.
The problem
Fjord water is full of particles. Put the torch next to the lens and you light up everything drifting between the camera and the thing you want to see. The picture turns into a snowstorm.
The fix
The arm is built as segments with ball joints, the same idea as a skid on an ROV: one frame, and the tool bolts on where you need it. Ball and socket print with 0.25 mm of clearance, and the friction comes from a split socket pulled up with an A4 bolt. That way the torch can be aimed one-handed and stays where it was put.
The torch has to have its own waterproof housing. The arm is only a mount. The material is ASA-CF, stiff enough that the arm does not wave about when the rig is drawn through the water. Remember that printed plastic with sparse infill is buoyant — every arm added has to be balanced with lead, or the rig hangs over. Film the same murky water twice, once with the torch beside the lens and once with it 25 cm out, and the point makes itself in twenty seconds.
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