Saturday, 15 February 2014

Understanding basic electronic flash modes on Micro Four Thirds cameras and TTL Flashes


A good friend asked for a work-together on figuring out his Olympus XZ-1 (pdf) and Nissin Di 466 TTL flash (pdf). It was confusing the heck out of him and after some early surprises, I was wondering about how it was supposed to work as well. So, this is for the beginner. If you are not a beginner, pass on this and visit Joe McNallyDavid HobbyMark Wallace to name a few gurus.

Approach: Auto Flash

Exposure Modes on the camera body

Typically there are following exposure modes – iAuto, Program Mode, Aperture Priority, Shutter Priority and Manual Exposure. Remember that without the flash, the camera in iAuto, P A or S mode will measure the scene light and adjust the f/no, shutter speed and ISO (if that is Auto ISO) for a standard exposure. With the flash fitted and both flash and camera switched on, even the M mode with Auto TTL flash will use calculations by the camera.

Flash menu icons on the camera body

Look for the Lightning Bolt (text describes this as Fill-In) – there is an implication to the description. It means
    • the flash will explicitly fire
    • the natural light of the scene will be measured with the camera’s chosen shutter speed, f/no and ISO settings.
    • will fire to top up the light..

Settings on the flash itself

Set the flash to Auto-TTL mode - on the Nissin Di-466 this means the Mode LED is unlit

What to set

To reiterate – put the camera on iAuto, P A S or M and the flash on Auto TTL. The camera will automatically calculate how much flash light to use to top up the available light.
  • This will be satisfactory if you are happy enough with the resulting exposure and don’t want to calculate or test anything.
  • If you find the resulting exposure is a little darker than you prefer (for example a person’s skin tone appears too dark), either
    • use the camera’s menu for flash +/- compensation to adjust brightness
    • use the +/- buttons on the flash body to adjust brightness

Reasons not to use Approach: Auto Flash

  • Even using the +/- compensation, the camera controlled flash is not outputting the full power of the flash. Remember, the camera first calculates the scene and then the human intervention is applied as an adjustment of the calculation.

Approach: Manual Flash

  • Set the camera body to M for Manual Exposure Mode.
  • Choose some starter settings for the camera body. For example, f/4, 1/100th sec shutter speed, ISO 200.
  • Set the flash to non TTL - full manual mode. On the Nissin Di466, that means the Mode LED should be showing a red colour.
  • Set the flash to medium power say 1/4 power. On the Nissin Di466 that means press the +/- buttons to light up half the power status LEDs.
  • Aim and shoot. Chimp, decide whether you want darker or lighter and adjust the
    • flash power
    • ISO
    • flash distance to subject
    • bounce or direct with diffuser
  • Rinse and repeat (no, not literally)

Reasons not to use Approach: Manual Flash

  • You can't afford the time and effort to chimp and adjust until satisfactory
  • Approach: Flash Auto is working fine.

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