Optimal distance from video light to lens to minimize backscatter

[undefined]

I hope this is the right place to put this thread.

I'm curious as to the optimal distance from the lens to the video lights in order to best illuminate a wide angle shot while minimizing backscatter. I have never used video lights before, and have been out of the water for the past decade focusing on other things in life. Heading to Maui soon and want to get good video of my son as he does his first dives and completes his open water cert.

The equipment I'll be bringing is a GoPro Hero 11 (2 of them, but one will be going without lights and just a red filter). For lights I've got a pair of i-Torch Venom 50s (5k lumen each, 120 degree beam) and a pair of Light and Motion Sola 15000 (15000 lumen each, 120 degree beam).

I'll be using a SRP tray and have several arms available, but in order to achieve neutral buoyancy I'm looking at using 8" arms with the Sola 15000s, which fully extended will put the lights roughly 12 - 13" to the side and 4" behind the camera lens. With the smaller Venom 50 lights, the lights will be about 14" to the side and 4" behind the lens. This is maximum distance, not minimum.

Is that enough to keep backscatter down?

 

[tursiops]

The issue is not the distance of the lights from lens, but rather the angle between the lights, the subject and the lens. It is called "Backscatter" for a reason....
Your goal is to turn the backscatter into side scatter, which is less efficient at scattering the light back into your lens.
If the subject is (say) 3 ft away, then you want your light like 3 ft to the side of the camera, This is difficult in wide-angle shots.
Your best bet in the scenario you describe is just to get the lights as far way from the camera as you can, and then get at close as you can (wide-angle helps with this).

You can get some benefit by not point the lights directly at the subject, but splay them ouwards so just the edge of the beam hits the subect.

Even better, don't use lights. Shoot with ambient light. AT the depth at qich an OW class happens, in MAui waters, there should be ample light. If you need color corretions, use a red/magenta filter and/or corect in pot-processing.
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By the way, videoing an OW class is often vetoed by the instructor as it can be intimidating to the students and make them nervous. Even if allowed, you may be so far away that the lights will be useless.

 

[undefined]

That's what I figured. The optimal position would be effectively to light the subject from the side such that any light reflected would be going back at an angle that did not hit the lens. I might not be up for a six foot wide camera rig

As for the class, I did check with the shop first and paid extra for a private instructor/class. My wife and I will be staying far enough away to avoid distraction. The goal is to let our son and the instructor focus on his skills, not on us.

 

[tursiops]

That's what I figured. The optimal position would be effectively to light the subject from the side such that any light reflected would be going back at an angle that did not hit the lens. I might not be up for a six foot wide camera rig

As for the class, I did check with the shop first and paid extra for a private instructor/class. My wife and I will be staying far enough away to avoid distraction. The goal is to let our son and the instructor focus on his skills, not on us.

My guess is ambient light will be the only possibility. And it is much easier!

 

[undefined]

My guess is ambient light will be the only possibility. And it is much easier!

I suppose I should have asked here before buying two sets of video lights.