see also:

• the Olympus OM-D system and how to make the most of it
• flash x-sync in Olympus digital cameras
• Olympus OM-D flash modes

• key shift is a photographic term used when the photographer chooses to under-expose the ambient light (eg sunlit scenes) and light the subject with artificial lighting such as a flash (although this needs either a very fast flash sync or very powerful flash units or close flash-to-subject distances if ambient is sunlight)
• the photographer may also choose to alter the color rending of the ambient light to create an even more dramatic effect

An example of key shifting with color shift using an Olympus E-M5 - note the deep blue trees in the background at midday while the subject has perfect white balance from the custom WB set to match the gel:

more from this zombies series and further details on how I achieved this effect here: http://www.ayton.id.au/wp02/?p=6606

• preferably have the subject in the shade - particularly if your flash is not powerful enough to overcome sunlit scenes
• attach flash and set to Manual
  • start with maximum output or 1/2 power
  • if you want to try pushing shutter speed faster than flash sync to try to overpower sun, you must connect flash to camera only via PC sync cable or via the central hotshoe pin
    • if you use a compliant flash attaching via the TTL pins, the camera will not allow you to increase shutter faster than the x-sync for that flash-camera combination!
    • thus can use a Canon flash directly, but if using an Olympus flash, must use a simple one-pin hotshoe adapter so the camera does not detect it is a compliant flash unit
    • of course, the flash cannot use TTL exposure, and you must resort to Auto or, preferably, just Manual flash exposure
    • with the OM-D's, a shutter of 1/400th sec will result in a small area at the TOP of the image not being lit by flash - this is fine if you have no subject there, at 1/500th sec, you have almost half the top not being lit by flash - this may still be manageable depending upon your subject
    • if you have a camera such as the Panasonic LX-100 which has a shutter inside the lens, it will sync all the way up to 1/4000th sec with full flash output and with full frame coverage (not Super FP or HSS mode which is useless for key shifting)
• set camera exposure mode to Manual
• set flash mode to Fill-In (even though it will be your main light)
• set aperture to your desired aperture
  • if you want a wide aperture for shallow depth of field (DOF), you will need to also use a polarising filter or ND filter in bright scenes
• set ISO to base ISO (eg 200) for best quality - may need to change this later
• set shutter speed to the fastest shutter speed possible
• now assess the ambient exposure - you are generally aiming to underexpose by 1-2 stops:
  • if the ambient scene is over-exposed you need to reduce ambient exposure by one or more of:
    • reducing ISO to LOW (ISO 100)
    • increasing aperture f/number (making aperture smaller)
    • using a polarising or ND filter
    • push shutter speed even higher as outlined above
    • move the subject to a less bright area
  • if the ambient exposure is too dark (as may happen when the sun is setting):
    • remove any polarising filter or ND filter or increase ISO - although these will require changing flash output
    • use a slower shutter speed - this has the advantage of not needing to change the flash output
• now assess the flash exposure
  • this is best changed by either:
    • changing the power setting on the flash
    • moving the flash closer or further from the subject
    • add extra flash units if still too dark

• set Menu:Cogs G:flash+WB item to OFF otherwise camera may default to autoWB even tjough you have set a custom WB
• choose a colored gel and place on your flash unit
  • use a full CTO (Color Temperature Orange) gel if you want daylight ambience to appear blue (can also use this to match incandescent lighting)
  • use a blue gel if you want daylight ambience to appear orange like a sunset
• perform a custom WB with the flash and gel aimed at a neutral target
• if using manual flash exposure be aware that gels will DECREASE the amount of light coming from your flash

Here, a blue filter was used on the flash with custom WB to simulate a lovely warm sunset in the background: