Backscatter Underwater

 Causes and how to avoid it in your photographs

By Scott Gietler

 
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The underwater photographer constantly has to worry about avoiding backscatter when using strobes, or especially when using an internal flash. Backscatter presents many challenges. Backscatter is mainly caused by strobes or the internal flash lighting up particles in the water in between the lens and the subject. It can also be caused by lighting up open water directly behind a subject. Backscatter is easier to see against a dark background. 

 

backscatter in underwater photo

This photo suffers from the dreaded "Backscatter" - which ruined a nice photo! Brown shrimp from Redondo Beach, Southern Califorina.

 

Strobe position to reduce backscatter

If you are a beginner in underwater photography, you may want to watch my video tutorial on reducing backscatter.

 

The most backscatter can be seen when a strobe is positioned right next to the lens, for example like the internal flash of a point and shoot camera. The backscatter will be worse when the subject is far away, or if the water is filled with plankton or sand. Shooting into open water also shows more backscatter than if a subject has reef directly behind it.

 

To reduce backscatter, photographers will use two strobes far from the lens, that light up the subject with only the edge of the light beams. A diagram showing this is also on the strobe diagram page.

 

strobe positon for reducing backscatter

This is the strobe position I would use for a fish 2-3ft in front of the camera, to reduce backscatter. Notice how the strobes are out wider and pointing out slightly. For a macro subject very close to the lens, I would pull the strobes in just enough so the edges of the cone touch the subject, but the strobes would still be pointing out slightly.

 

Backscatter from yourself and your buddies:

 

In sandy and silty environments, the cause of backscatter is often your own fins, or your buddy’s fins. The following will help:

  • Make sure you and your buddies have good buoyancy, and frog kick around photo subjects instead of flutter kicking
  • Stay downcurrent of the photo subject
  • Discuss the concept of personal space with your diving buddies. Make sure they wait for their turn to shoot a few feet away, downcurrent of the photo subject.
  • Dive with others who have mastered frog-kicking
  • If a current is pushing you towards your dive buddy, use a Lembeh stick to avoid having to fin to change course. This can greatly reduce backscatter and underwater collisions

 

Preventing backscatter in a compact camera

In a compact camera, you are often using the internal flash. Use the diffuser to reduce backscatter in your photos slightly. The best solution is to get an external strobe. Make sure you completely block your internal flash after getting your external strobe, otherwise there will still be backscatter from the internal flash. Duct tape on the outside of the housing works well.

 

Top tips to prevent backscatter

  • If you have external strobes, use proper strobe position. Bring your strobes out wide, away from the port, and don't point them towards the subject, just light the subject with the edge of the cone.
  • Take photos far away from other people
  • Use proper fins, learn frog-kicking technique, acheive perfect buoyancy
  • Only take photos within a few inches of your port, either in macro mode, with a macro lens or with a fisheye lens.
  • Find areas of the dive site with better visibility, which is often right near the surface, down deeper, or in a protected area of the reef
  • Dont' shoot against the open water, shoot at a subject with reef directly behind it. This can be very effective.

Strobe aiming lights

Some strobes come with built in focus lights, or aiming lights. I almost never have those pointed directly at my subject, unless I'm shooting supermacro, or I'm shooting in very clear water, or I need to light up a subject in a cave and my focus light isn't doing the job.

 

Removing backscatter in Photoshop

You can read about editing underwater photos using Photoshop.

 

Further Reading

 


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Comments

What's a Lembeh stick?

What's a Lembeh stick?

I have a Sea and Sea strobe

I have a Sea and Sea strobe that the sensor simply "covers" a part of the internal flash area on the housing. Should I be blacking out the remainder? I am still getting used to moving the strobe farther out for less backscatter. Any feedback is greatly appreciated. the strobe has a TTL setting, but it doesn't really seem to work with the way it senses light right now

In my experience, I've found

In my experience, I've found that using a strobe "mask" works best to block out the camera's internal flash (I'm assuming you're using a compact camera with the internal flash located on the left).  These can be purchased online.  The mask is adhered to the housing, and includes a small "port" for your fiber optic cord.  Make sure your strobe and camera are both set to TTL.

Michael Zeigler [url]http://www.seainfocus.com[/url]