I just spotted this image on the BBC News site. (I’ve linked it from the BBC website – let me know if it vanishes!)

Look at the photographer holding his camera in the air behind the red-haired lady.

He has a CTO (Colour Temperature Orange) gel attached to his flash; the lighing where he is shooting is probably tungsten (light bulbs, basically) so he’s gelled his flash to match.

As a Canon user he will set his camera white balance to Tungsten. Nikon call this Incandescent but the icon for them both is the same – the little bulb (). He does this so he can get both ambient and flash in his exposure and not have uneven lighting – the ambient light and the flash light are the same colour.

If he didn’t do this, the people lit by his flash would be white (becuase flash is daylight balanced) and those not lit by flash would be yellow (becuse tungsten is very, very orange).

What he needs to be careful of is heading where the ambient isn’t tungsten, such as outdoors. What would happen then is that the portion of his shot lit by flash would be colour-correct but everything else would turn very blue. Check out this shot from Flickr that illustrates this perfectly.

The person who took this photo didn’t gel his flash and that’s why the people at the back look so much more orange than the ones in the front. :)

More on using gels for color correction at The Strobist.

Where to buy CTO gels in the UK

I buy them in 50x60cm sheets from the Rosco e-color range. I find the number I want from here and then call Flint’s Hire and Supply in London on 020 7703 9786 and ask them to order them for me. They take a few days to show up and cost about £3 each.

You can also buy them from The Flash Centre (sold by the sheet, ignore the crappy website – just call them or visit the shop) and Direct Lighting (sold by length).

Update

See an example of using a gel to intentionally turn up the blue in the ambient part of your exposure here.