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Jarviz

Help with backscatter on one side only

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We are have problems with backscatter from one strobe.

We are using a D70, Ikelite housing, Nikon 10.5 lens, 2x DS125 strobes 16+ 6inch strobe arms both sides.

We have the stobes pointed slightly out and have pointed them even more out but the problem is still there.

Below is a RAW image with the backscatter on the upper left.

This ia a crane that fell off a barge in Lake Ontario @ 140ft.

Any ideas how to solve this problem??

 

RAWcrane.jpg

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dive in clearer water..

 

seriously, this is a common problem, the 10.5 is a very wide lens, and its easy to get backscatter with them, especially when shooting things far away..

 

if the subject is far away, unless your arms are super long, or the water is ultra-clear, you'll get some backscatter..

 

usually its manageable however...

 

from your photo, it looks like your left strobe is forward a little too much, try pulling it back a little bit.. I got a bright spot like that when my strobe was forward too much.. the 10.5 lens is so wide, it's able to "see" the burst of light directly in front. the strobes have to be pointed out, but its even more important to be back far enough.

 

hope this helps,

scott

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seems that the relative positioning of the left strobe is different than the right. find the difference.

 

do you have a dome shade? if so, lower the strobe so that its behind the middle shade flap. the corner of the frame is where the fisheye lens sees the most.

 

remember that diagonally corner to corner, the 10.5mm sees 180 degrees. All strobes will produce a 'burst' of light (as scott said above) up to about one foot or so in front of the strobe, so if the strobe is in the top corner less than one foot back from the plane of the dome (from the lens' front element) - voila! - a burst of backscatter in the corner.

 

this is not uncommon, I still get the same thing in my 10.5mm pics when i'm not careful, even in clear water. Cheers,

 

Chris

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I'll bet from what I see that the strobe position is set at 45 deg to the housing....at a guess ...slightly forward. where the strobes need to be is behind the dome port...behind the shades...close to the centre line of the lens....with the strobes pointing out slightly. This is to use only the edge lighting of either strobe..... I have 132 deg WA and , using this technique I get virtually zero backscatter regardless of visibility conditions. I have shot effective close focus WA in vis of less than 5m. Martin Edges book "The Underwater Photographer " Third Edition , has some remarkable insight into this subject.....you dont need 2m of arms to get a good result

 

Chris

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Chris, I believe is correct. While its not "backscatter" the lighting up of particulate is a pain. When I had one strobe this happened all the time. Since adding a second strobe, I usually place the strobes behing the camera and angle both strobes out to feather the subject with the edge of the strobe. This usually gives me a satisfactory photo even in tough conditions.

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Welcome to Wetpixel Jarviz.

 

dive in clearer water..

 

Looks pretty dam clear for Lake Ontario water to me. :guiness:

 

Physically pull the flash head back and further behind the front element of the lens. As others have said, the 10.5 mm wide angle lens is a challenge to work with.

 

For what it’s worth, I have found that there is a “sweet spot†for the placement of your strobes that will reduce your particulate problems dramatically. I’m still working on finding that exact spot with my camera rig, but as others have said: flashes pulled back, angled outwards and lower than usual from the 45° upper corner frame position.

 

Have you removed the lens distortion with Nikon Capture? Sometimes the particulate backscatter can be eliminated when using the fisheye distortion tool in Nikon Capture.

 

By the way, is this the crane that is over by Oakville? Haven’t dove it yet, but it looks interesting. Looks cold and dark too.

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Try 1 or more of these:

 

Try to have the front of the strobe behind the back of the housing plane, hot spot will be out of the photo

 

Use a slower shutter speed and turn down the power of the strobe, will lessen back scatter.

 

Photoshop, if all else fails

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