Sunday, 8 May 2016

Colour Temperature (Part 1)

Creating contrast with colour temperature

Whilst there is the obvious contrast that can be created by using a harder light source, we can also create contrast of a different kind by playing around with colour temperature. This gives a different feel to the photo and it's just one way of affecting the mood of an image.

As with all the images in this series, the photo at the top was created using just a single, off-camera flash. It's fairly subtle, but the background has a definite blue colour cast to it whilst the subject is correctly lit. The wall is not that blue, and there was no gelled flash on it. It's possible to make it much more extreme than this shot shows, but I wanted to keep it subtle... so, how's it done with just one flash?

The Lighting

Here's the lighting diagram for the shot, which we'll discuss after the picture...

Looks pretty easy, just a single flash firing into a silver umbrella - but there's something else going on that you can't tell from this diagram.

The cool blue tone for the background was created by adjusting the colour temperature on the camera, then gelling the flash head to compensate; this ensures that the colour of the ambient light is changed but as we've corrected for the light on the subject, the subject is correctly lit.

How's It Done?

It's a simple effect to achieve but you will need a coloured gel to do it. The gel is called a CTO gel (Colour Temperature Orange, or Colour To Orange). Here's what you do...

  • Set the colour temperature on your camera to tungsten, or somewhere around 3400K.
  • Get your exposure for the ambient light - either use manual exposure or aperture priority mode (but ensure that the shutter speed does not exceed the flash sync speed for your camera. This is typically around 1/160th - 1/250th for many cameras, but check the manual for your camera).
  • Set your flash / strobe / speedlight up (I used an umbrella for this, but you don't need to). Place the CTO gel over the flash head; you may need a little bit of tape just to keep it in place.
  • Try a test shot - you may need to either adjust the power of your flash / strobe / speedlight, or move it around a bit to get the flash exposure correct for your aperture setting.
  • Errr... that's it!
In the next post we'll take a look at how this works.

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