Thursday, 30 October 2008

[strobist] Balancing Ambient

Unless you are shooting at the golden hours (just after sunrise and just before sunset) then it will most likely be you will be turning to this technique -- your flash will become the main light for your subject and the ambient becomes fill.

This involves getting a correct base exposure AND THEN underexposing it by 1 or 2 stops (whether by shutter or by aperture) - the flash is then brought in to provide the main light at the correct exposure.

you can:

Using max sync, exposure for the ambient using aperature

Bringing your flash in to light the subject adjusting as you wish we have our scene. The problem with this method, is that you are already a max sync so you can not drop the shutter any further so a scene at f5.6 @ 1/250 needs to be adjusted by closing down the aperature (less light) so have to open the shutter (compensate for the lesser light)

ie. original exposure f5.6 @ 1/250 with flash 1/8th power
f5.6 -> f8 -> f11
1/250 -> 1/125 -> 1/60th (2 stops)
1/8 -> 1/4 -> 1/2 power
and now we have f11 @ 1/60 with flash 1/2 power for the same exposure, incl flash lit subject. We have moved 2 stops so we have the ability to dropping the ambient by 1 or 2 stops depending on the required mood of the final exposure.

Select the DOF you require (via aperture) and then getting the exposure of the ambient correct with shutter

Again, bringing your flash in to light the subject adjusting as you wish we have our scene. This is a little less work but without the max sync, we are possibly making more work for the flash (higher output)

As a side note, the darker the ambient becomes, the moodier it gets and more dramatic the final image.. this may not be suitable for all contexts and going too far past dramatic makes it look like you've just flashed your subject in the middle of a black hole.

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