Black Backgrounds

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Postby Durham Diver » Thu May 20, 2010 1:54 am

When you are shooting for black background subjects I understand you need to shoot up, use a fast shutter speed and small aperture to minimise ambient light effect, but would you also pick a low asa - say 100 ? minimise noise and also reduce ambient light?
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Postby tswinner » Thu May 20, 2010 7:10 am

Water does not reflect light. Unless there is a lot of particales in the water. :D
The key to a black background is light only the subject with your strobe and none of the surrounding reef.
Your shutter, aperture and iso all need to be set so they are not affected by ambient light.
So the short answer is yes a low iso will help in most cases.

Best,

Todd
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Postby scottg » Thu May 20, 2010 10:22 am

It really depends on how much ambient light there is. If there is lots of ambient light (sunny day, shallow water), decreasing your ISO and increasing your strobe power will help.

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Postby James » Thu May 20, 2010 10:48 am

Expose for the near subject with your strobe and f stop, expose for your desired background with your shutter speed selection.

No shutter speed you select will be nearly as brief as an electronic strobe pulse of 1/20,000 sec or more. Therefore your aperture (f stop) you select largely controls your subject and near exposure. The shutter however remains open longer than the strobe pulse and continues to expose the "scene" so following this logic, a quicker/faster shutter speed will produce a darker or increasingly under exposed back ground.

Obviously the background exposure is also a function of the f stop so selecting a smaller f stop with the faster shutter speed, but still an f stop that your strobe can produce a proper subject exposure will give a darker, under exposed back ground.

As to ISO/ASA most strobe exposures are calculated on ISO 100 setting I think, going to a lower ISO setting in your camera, such as 80 or 50 etc would require you to compensate your subject exposure by dialing up your strobe power by 1/2 stop or a full stop.

I probably did not say all that as well as I could but I am distracted at the moment, you get the idea.

James
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Postby Durham Diver » Thu May 20, 2010 12:05 pm

Thanks for the advice guys, much appreciated
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Postby bvanant » Thu May 20, 2010 2:45 pm

Durham Diver wrote:When you are shooting for black background subjects I understand you need to shoot up, use a fast shutter speed and small aperture to minimise ambient light effect, but would you also pick a low asa - say 100 ? minimise noise and also reduce ambient light?

One technique that can work if you can't get the space to shoot up is to use inward lighting where the strobes are only aimed at the subject but not at all at the background.
In the lighting discussion on this board or in Martin Edge's book you can find some tips on how to get there.
Bill

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