If I’m in a situation
where I want to use a flashlight outside during the day, and the natural
lighting is fairly bright, I might quickly hit upon a problem. For
instance, if my ISO is low at 100 and I want to use an aperture of ƒ4, those
settings will not produce a darkened sky and background as my camera's flash
sync speed is limited to 1/200 of second. Taking the photograph at those settings with a shutter speed of 1/200 will give me an overexposed image.
The ISO has been taken
as low as it can and I want to use a wide aperture to give me a shallow depth
of field, blurring the background. This leaves me with one option, to
increase the shutter speed beyond the camera’s sync speed of 1/200th, and this
can be achieved by using the high speed sync setting on the flash. This
setting enables me to use a faster shutter speed and the flash will compensate
for this, so that all the power of the flash is captured in the shorter time
than the shutter is open. If high speed sync is not used, then part of
the frame will not be lit by the flash and a blurred black line will appear at
the edge of the frame because the camera has not been able to capture all the
necessary light due to the shutter coming into frame. When photographing
‘Contre-Jour’ it is important to get a good blend of ambient and flash light,
this does of course depend on the desired effect. Using softboxes and
umbrellas can limit the effect of the subject appearing superimposed. By
altering the shutter speed I am able to control the effect of the flash and
allow more or less ambient light into my background without effecting the flash
light on my subject.
Flashlit image, taken at the above settings
Ambient image taken immediately afterwards
