Avoid backscatter with single video light possible?

I'm dabbling in UW photography and video and, among other things, bought a single 6000 lumen video light, just to experiment. It's 120°, has a good CRE rating (90) and the test footage from my TG-5 is acceptable in terms of colour rendition. However the backscatter is terrible and I'm assuming it's to do with the position of the light. I had it mounted to the side of the housing pointing straight ahead (probably my first mistake), shooting general scenes of reefs etc from around 2-5m distance, focal length 25mm.

I've tried searching for the best position for a single video light but most search results are for avoiding backscatter for stills, or for two video lights (ie on the side pointing out).

Am I asking too much when trying to use a single video light for such scenes, or is it possible to avoid backscatter with a single light? If so, what's the optimum position for it?

Thanks.

I think showing us some footage would allow us to diagnose your issue more accurately?

Ultimately, most backscatter is caused by particulate in the water...

Hi Adam,

I'll try and do this, though I'm on the water atm and out diving again tomorrow. Was hoping for a quick answer before my next dive!

I would suggest pointing it out progressively - try a few stills shots when you first drop down, point it away until you lose the lighting then bring it back so you just get light on your subjects.

Stills and video are not fundamentally different - if you light up particles they will show up in both stills and video.  this link has some coverage of a single strobe.  Fundamentally you want to keep the bright part of the beam (close to the light)  away from the lens/dome.  https://www.opticaloceansales.com/files/OOS-Strobe-Positioning.pdf

2-5m is probably stretching the friendship a little for a video light I would suggest - however if you a re video-ing distant stuff you want the light a long way off on a long arm.

25 minutes ago, demonboy said:

Hi Adam,

I'll try and do this, though I'm on the water atm and out diving again tomorrow. Was hoping for a quick answer before my next dive!

"shooting general scenes of reefs etc from around 2-5m distance" is the first problem. You have to go closer to have effects from your lamp. 

Imagine the cone of light. It should illuminate the subject but not the water between your camera and the subject (as much as possible) to avoid backscatter.

A single light I would position on the top af the camera on an arm (but far from it) and try to tilt upwards and check the effect.

13 minutes ago, ChrisRoss said:

I would suggest pointing it out progressively - try a few stills shots when you first drop down, point it away until you lose the lighting then bring it back so you just get light on your subjects.

Stills and video are not fundamentally different - if you light up particles they will show up in both stills and video.  this link has some coverage of a single strobe.  Fundamentally you want to keep the bright part of the beam (close to the light)  away from the lens/dome.  https://www.opticaloceansales.com/files/OOS-Strobe-Positioning.pdf

2-5m is probably stretching the friendship a little for a video light I would suggest - however if you a re video-ing distant stuff you want the light a long way off on a long arm.

Very nice descriptions in the recommended file. Actually, I would try position a single lamp as shown in the first picture of the pdf (and would fine tune from there)

Thanks for the suggestions. Funnily enough I'd just downloaded that PDF not half an hour ago. I have two, maybe three dives tomorrow, so I'll apply one position for each dive.

I'm going through the same process with my strobe (Inon S2000). Despite having two strobes I only have one YS mount so I'm attempting single strobe macro and that PDF suggests pointing upwards to avoid backscatter, so I'll try the same technique with the video light. 

Thank you for your replies, it's much appreciated. If I have any luck I'll post up my results but in the longer term I'm saving up for a second video light.

Hi again,

I said I'd post up a video clip of the offending backscatter and forgot I'd put the clip up on Instagram. You can see it here.

Since then I've taken a few more clips but been angling the light away from the camera. It helps a little but I did another dive today up the coast and the water was generally clearer, so I do wonder if there was an excessive amount of particles in the octopus clip.

9 hours ago, demonboy said:

Hi again,

I said I'd post up a video clip of the offending backscatter and forgot I'd put the clip up on Instagram. You can see it here.

Since then I've taken a few more clips but been angling the light away from the camera. It helps a little but I did another dive today up the coast and the water was generally clearer, so I do wonder if there was an excessive amount of particles in the octopus clip.

Keep in mind you can minimise backscatter, but probably not eliminate it completely.  Any particles right next to the subject are going to be lit same as the subject.  In video as long as it's not a snow storm it's probably not a major problem, equally you don't want big out of focus blobs wafting in front of your subject and these are a lot more avoidable.  Of course you there are a number of things to help avoid backscatter not least of which is good diving practices to avoid stirring up particles.

Yes, I'm getting better at avoiding stirring up the sand myself. I'm frequently diving with another photographer so we're conscious of not messing up the shot for our buddy, but this clip was shot on a busy dive and there was a queue of people lining up to get this octopus, which could explain some of the backscatter.

If I can I'll post up another clip of the same dive where there should have been no or little backscatter.