Strobe and Backscatter

[Scubapauly]

Hi all,
Just been for another play in the pool with my kit. There was loads of muck in the pool tonight, think someones been eating bread in the pool lol was nasty.
So the question is......
I still seemed to get lots of backscatter, no matter where i moved the strobe. Is this right? I know there was lots of stuff in the water but shouldn't the strobe cut down on the backscatter. I tried the strobe all over from way out to the top left moving it all the way to top right and still got quite a bit.
Or am I just expecting too much?

 

[ScubaRon]

If there are lots of suspended particles in the water you cannot avoid some backscatter. But moving your strobe away from the lens should reduce it significantly. Did you have your internal strobe covered?

 

[Scubapauly]

Wow fast reply lol. Yeah it was covered, I used the sticker that comes with the D-180. Just didn't seem to matter where it was located, tried different angles. Guess thats just a lesson in how many particles are too many.

 

[justleesa]

Hi Pauly!
There was this filter delivered with your strobe. When you have that on your cameras internal strobe it reduces that light that's close to the lens, thus reducing the backscatter.
I don't know your experience with strobes ( an am a total newbie), so I'll just include some thing that I read on backscatter the J & C C hurch book "Choosing and using underwater strobes":

"There are two key concepts you must understand if you are to master the techniques of aiming the strobe correctly. First, you must overcome the problems caused by suspended particles in the water. Second, you must aim the strobe at the subject's actual position. Let's examine these concepts in greater detail:
1) When the strobe flashes, light from the strobe strikes suspended particles in the water and reflects back to the strobe. If the strobe is near the camera lens, the light reflecting from the particles passes through the lens. This causes little bright spots to appear in the picture. To avoid backscatter, you must hold your strobe away from the camera lens and aim it at an angle to your subject.
2) Underwater you see subjects one-fourth closer than they really are. For example, a diver that is actually 4 measure feet away appears to be only three feet away. So when you are aiming your strobe by hand-eye coordination ( by the feel of the strobe arm in your hand), you automatically aim the strobe at the subjects apparent position that you see. How ever the subject isn't there. The subject is 1/3 further away."

It goes on to say "by directing the beam of light in from the other side and cutting the edge of the beam just in front of the subject, the effects of suspended particles are minimized. The light is reflected away from the camera lens. This is a key lighting technique for turbid water. With a wide-beam strobe you may have to aim the strobe behind the subject to cut the edge of the beam just in front of the subject."

Hope this isn't too much Yada yada and is of some kind of help.

Aloha,
Lisa

PS: I like the empty wallet part - sounds familiar

 

[ReyeR]

Wow fast reply lol. Yeah it was covered, I used the sticker that comes with the D-180. Just didn't seem to matter where it was located, tried different angles. Guess thats just a lesson in how many particles are too many.

Strobe aim is critical to control backscatter. Ofcourse in some situations you can't eliminate it completely but you can take steps to minimise it. Here are a few good webpages:

First, understand why backscatter happens:
http://www.daveread.com/uw-photo/strobes/aim.html
http://www.barrylipman.com/Photogs/BS/BS.htm
Some good tips here:
http://www.kelpfish.net/strobe.swf

 

[justleesa]

Strobe aim is critical to control backscatter. Ofcourse in some situations you can't eliminate it completely but you can take steps to minimise it. Here are a few good webpages:

First, understand why backscatter happens:
http://www.daveread.com/uw-photo/strobes/aim.html
http://www.barrylipman.com/Photogs/BS/BS.htm
Some good tips here:
http://www.kelpfish.net/strobe.swf

Great pages! Thanks ReyeR

 

[Abril]

I had the same affect in a pool. Had to take pics of a scuba class and couldn't get a single good shot. But in the ocean it's a different story. I just thought it had something to do with the pool. Skin flint, cloths flint really how often do they clean those things?

 

[Scubapauly]

Thanks for those pages ReyeR, nice tips. Guess its still part of the learning curve. Was more interested last night in getting the subjects properly lit. Some more practice at aiming the strobe is needed now I guess.

Abril - It did make me wonder about how often the pool is cleaned, the things those swimmers never see huh

 

[louisianadiver]

Hi Scubapauly. First, good for you for experimenting in a pool. Backscatter is a strobe effect, and it can be minimized by aiming your strobe and controlling your exposure. Make sure that your strobe is not aimed to hit the water in front of your subject. Remember that a subject 3 apparent feet away underwater is actually 4 feet away, so make sure that your strobe is set to hit a subject 4 feet away. Using 2 strobes will allow you to hit the subject from wider angles, which minimizes backscatter. Aim the strobes so the beams intersect at the subject. An example of this can be seen at http://claycoleman.tripod.com/id47.htm The turtle is completely lit with no backscatter, but the lighting is a bit flat--a problem that could have been corrected by varying the power of each strobe. I think the best way to combat backscatter is to light most of the scene with ambient light and add only enough strobe light to give color and definition, as in http://claycoleman.tripod.com/id48.htm You can also concentrate your strobelight on a small portion of a scene, as in http://claycoleman.tripod.com/id43.htm Only about half of the turtle is lit by the strobe. Another way to minimize strobe light is to get very close. The photos at http://claycoleman.tripod.com/id79.htm and http://claycoleman.tripod.com/id124.htm were shot from 1 foot away, and only a dash of strobe was needed to light them from that distance. The ambient light was also lightened (by slowing the shutter speed) in the photo at http://claycoleman.tripod.com/id79.htm A lighter background will camouflage backscatter. I use 2 strobes to completely light a subject with strobelight in front of a dark background, as in http://claycoleman.tripod.com/id126.htm Backscatter is much easier to manage with 2 strobes. If you want to forget about backscatter even in dirty water, try turning off your strobe and shooting a silhouette as in http://claycoleman.tripod.com/id61.htm

 

[Scubapauly]

Wow lovely pics and thanks for the tips Louisianadiver. I think the big mistake I made was aiming the strobe AT the subjects. Done some reading since and with the tips from here will hopefully make a bit of a difference next time.
Have booked some UK dives for this weekend, will hopefully get one good pic lol