Wednesday 7 January 2009

Wedding Photographer Kent - Flash Gels

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A question on correcting the colour temperature of flash light today.

Hi David,

Do you use much gel correction in your work. I'm still trying to understand when to use it ideally. If your room has halogen bulbs, what do you use?


First off, please read an earlier post on flash colour temperature. Flash light is balanced for noon daylight (5600K), so adding fill flash on a sunny day requires no correction. When shooting indoors, however, the ambient light you are most likely to encounter will be due to incandescent or fluorescent light bulbs. Incandescent bulbs generate light by passing an electrical current through a tungsten filament which then emits light as it becomes hot - the colour temperature of the light is related to the temperature of the filament, it is a black-body radiator. These bulbs contain either an inert gas (as in typical household bulbs with a colour temperature of 2500-2800K) or a halogen gas (as in halogen lamps, 3000-3200K). To correct for this you would typically use a colour temperature orange (CTO) flash gel - see one fitted to a Speedlite. They come in various strengths, but in my experience, the most useful is a full CTO gel.

Fluorescence is an entirely different process for light generation and it makes no sense to talk about colour temperature. The key thing for a photographer to know is that it gives your images a green tint - hence you attach a green gel to your flash to match this. In post-production you can then remove this green colour cast from the image.

Whether you balance the colour temperature of your light sources is a creative decision that you're free to make - there are no rules! A couple of examples:

In the shot above you can clearly see that the flash light is much cooler than the ambient lighting - no colour temperature correcting gel was used. It was a Xmas wedding, it was freezing outside and so I decided to give the shots a warm atmosphere - a 'cosy feel'.

In the shot above the flash light has been modified to match the ambient halogen lights - notice the blueness of the evening light coming through the sky light.
Hope this helps.
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