The old question - diffusers or not for murky water...

I know it's an age old question but thought I'd bring it up again...

Basically, with murky water, do strobe diffusers make backscatter worse or better?

I've been trying to work it out and test myself with no clear answer.

I'm using 2 X DS160 ikelites so are fairly powerful and also have a nice, big, circular flash bulb unlike some of the others. Shooting WA with a 10-17 tokina.

Ultimately I am finding I get far more backscatter around the edges with diffusers than I do without.

The obvious downside is the trickier positioning needed to not leave centre shadows.

When I put the supplied manufacturers diffusers on the edge backscatter seems to increase. I also lose over 2 stops of light which means I need a near full power dump for a diver sized subject located a metre away (I know, get closer but divers don't always allow it!). I assume edge lighting drastically reduces the light put on the subject?

I've also got the ikelite dome diffusers but finding backscatter is even worse with these.

Using standard 9-3 or 10-2 strobes with the head roughly in line with the handles. Positioned straight ahead (or out slightly if close) and arms about the subject to dome distance apart. Subjects roughly 1m or less from the camera.

So I'm just wondering what are people views for diffuser Vs non diffuser for murkier water?

Is my technique drastically wrong to be getting more scatter on the edges with them or not?

Or more in general what are peoples recommendations for wide angle in murky water? (I have to dive Myanmar a lot where 2-3m of dark, green, sediment full water is the norm)

I've done hundreds of dives experimenting here but still have issues. I'm finding none is better, everything I'm reading online says the opposite so possibly is a technique problem. The 2+ stops light loss is an issue too preventing multiple shots in a short time.

Any thoughts?

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Lots of people suggest things online they haven't actually tried. If you find less backscatter without diffusers, then go without! Makes sense to me. They're certainly not required with a circular flashtube strobe like the ikelites.

Narrower beams are definitely better in murky water, I'd say as narrow as possible while still covering the area you want. The idea is to get light onto your subject but not the water between the lens and subject.

Diffusers increase the angle of coverage which means with the same arm length the beams will meet closer and if the subject if further away produce more backscatter

If you cant get closer increase the length of your arms or if this means you don’t have enough light or you don’t have longer segments stay without diffusers and tune the working distance

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Poor visibility means that you need to control where the strobe's light is going!

All diffusers are designed to reduce the strobe output and to widen the beam. Assuming that you can turn down the strobe's output sufficiently, or can pull the strobe's back away from the subject, diffusers are typically more of a hindrance in murky water!

Dome type diffusers are particularly troublesome in this regard

In terms of your specifics, I think you are probably relying on your strobe's for lighting too much. You don't mention your set up or camera settings, but I would be pushing up the ISO, stopping down and slowing the shutter speed. If you are finding that your Ikelite strobes with a diffuser aren't providing sufficient light at 1 meter away, I would suspect that there is something else at work. DS-160s are powerful beasts!

All the best

Adam

I find it helpful to separate the issues of backscatter and diffusers.

1. Think of backscatter as a function of light intensity aimed at the water column between your lens and your subject. The closer your strobe is to this column of water between your lens and subject, the more intense the light will be. The more you aim your strobe at this water column, the more intense the light is. You need to adjust your strobes such that their beams light as little of that area as possible, usually by pointing them outwards or by reducing intensity.

2. Diffusers change the beam shape and widen the beam's coverage. Knowing this, adjust your strobes according to #1.

One more important fact to understand: light output from your strobe is most intense at the strobe (all that light is packed into a few inches of strobe tube surface) and dissipates very quickly as it travels through the water column to your subject (several meters wide for WA).

The reason some people say diffusers help is because they reduce the intensity of the light, but that's only half the equation (forgetting about position). The reason some people say (or experience) diffusers are worse is because of the diffuser pushing more light LOCALLY close to the strobe. If the strobe is close to that water column, all that intense light will light up backscatter.

The solution for WA? Pull your strobes several inches behind your housing. This gives the light some distance to lose some localized intensity and not intensely light up those backscatter particles. Works wonders in 3m-6m visibility. Oh, feel free to use that diffuser, because that's what'll get you smooth lighting for WA.