Wednesday, 29 October 2008

[stobist] Learn it, Learn it now

There aren't many ways to control light using your camera.. you can change shutter, change the aperature and ermm, do both. But thats the great thing - thats it!! With one of these you have control of your lighting situation from camera.

  • shutter - this controls the amount of ambient light available to the sensor
  • aperature - this controls the amount light available to the sensor whilst the sensor is exposed
Now here comes the science:
  • to lighten/darken the ambient lit but NOT the flash lit area, change the shutter speed
  • to lighten/darken BOTH ambient AND the flash lit area, change the aperature
  • to lighten/darken flash lit area but NOT the ambient, change the aperature AND send the shutter speed the other way
A previous article going through the affect of shutter and aperture is here

The Strobist Lighting 102 article is here

What we're talking about is better described in examples; the first 2 principles are simple so lets consider the use of aperture+shutter.

Consider that we have a correctly exposed scene at f11 @ 1/125th - the flash setting is not important except that it is exposing the subject @ f11

We decide that, w/o changing the flash, we want to increase the intensity of the flash lit subject. So whats it to be?

... the aperture needs to be openned up (to allow more light, incl ambient light to the sensor) but we have to compensate by dropping the shutter speed (to restrict the additional ambient light exposed to the sensor)

And the numbers:
f11 -> f8
1/125 -> 1/250
This results with the same ambient exposure but with the new increased intensity on the flash lit subject

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