Thursday, 30 October 2008

[strobist] 101 in a Nutshell - The Starting Point

Whenever we are balancing for a scene the strobist site recommends the following the same basic strategy for all shots:
  • get to max sync
  • get correct exposure using aperature

Now think about it, the max sync means the sensor is exposed for a shorter period of time to the ambient (essentially trying to kill it) so the strobe has less light to overpower.

Given the correct exposure we bring in the flash on manual; for indoors, i generally start at 1/16 or 1/8th power and outdoors upwards of 1/8 or 1/4. shoot and chimp (as DH would say) and adjust for the flash lit subject accordingly either by:
  • dialling the flash up/down
  • moving the flash in closer/further away from subject (be aware of the increased falloff if brought in closer)
  • changing the aperature and sending the shutter the other way; we will talk about closing down and opening up (ie f8@1/250 -> f11@1/125). Think of the shutter speed as openning up to infinity if that helps
... and again (repitition makes for learning I was told)

Subject too bright?

Power down the flash for faster recyle OR move it further back OR close down the aperature and open the shutter (ie f5.6 @ 1/250 -> f8 @ 1/125)

Subject too dark?

Power up the flash OR move it closer OR if we're not at max sync, open up the aperature and close down the shutter (ie f8@1/125 ->f5.6@1/250)

But what about DOF, arent we possibly missing out if we in low light conditions (ie aperture is more wide open)? This is possible, but if you're doing portraits the shallow DOF maybe what you should be looking for anyway.

However, since this is just a strategy, you dont have to follow it to the letter - use a compromise of dropping the shutter speed and correcting aperature for the given DOF you want OR by adjusting AFTER we have the correct exposure at max sync.

ie. we have our exposure at f8 @ 1/250 max sync
f8 -> f11 -> f16 (2 stops)
1/250 -> 1/125 -> 1/60 (2 stops)
We're now got greater DOF, f16 @ 1/60 but the flash will have to work harder to light the subject at f16 (pushing the power up 2 stops)

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