What do colour filters do? How does the red-eye reduction function work? Is there anything you need to do about the white balance setting when you use a flash? This article helps you to pre-empt and tackle issues to do with uneven lighting colour during flash photography. (Reported by: Masakatsu Nagayama)

 

Feature 1: When do you use a colour filter?

Colour filters come in handy when you want to adjust the colour temperature of light from the flash.

Colour filters are sold as accessories for external flashes. They come in the form of a semi-transparent coloured panels, films or sheets which can be attached to the flash head for use.

The colour temperature of an external flash is usually close to that of sunlight. However, there are times where you might want to use light that is of a different colour temperature, such as light that is more similar to tungsten light or fluorescent light. This is when you use a colour filter.

One common scenario where you might want to use a colour filter is when the ambient light in the place where you are shooting has a different colour temperature from the flash light. In your resulting shot, the colour will be uneven: The area covered by the flash light will take on the colour cast of your flash light, whereas the area not covered by the flash light will not be affected by it. 

Some photographers might purposely create this look for creative reasons. However, if you want the lighting to be evenly coloured throughout, you would need to "cancel" out the colour cast of your flash light by using a colour filter closer to the colour of the ambient light. 

 

 

Colour filters that are bundled with Speedlite 600EX II-RT

 

When shooting under a light with a different colour temperature, using a colour filter similar to the ambient light narrows the colour temperature difference. 

For a creative way to use colour filters on a flash, check out:
Cosplay Photography Techniques (4): How to Shoot with Coloured Light

 

Feature 2: What is the red-eye reduction function?

When you use a flash to take a portrait photo, the pupils of your subject might appear red in the resulting image. This is known as the red-eye effect. The red-eye reduction function reduces that effect.

What causes the red-eye effect?
Red-eye effect tends to happen especially when you use a flash in low-light conditions. The low light causes the pupils to dilate. When the light of the flash passes through the dilated pupil, it reflects off the blood vessels at the back of the eye, which makes the eye appear red in the shot.

How does red-eye reduction work?
When the red-eye reduction feature is enabled, a preflash will be fired when you half-press the shutter button. This triggers the pupils to shrink before the main flash is fired, which helps to reduce the red-eye effect.

However, do note that there might be other factors contributing to the red-eye effect, such as shooting conditions and factors related to your portrait subject. Hence, the red-eye reduction function on the camera might not completely eliminate the red-eye effect.

 

Feature 3: Which white balance setting shall I use during flash photography?

“Flash” or “Daylight” can be used as a reference when determining the white balance setting.

The Auto White Balance (AWB) should be able to achieve the appropriate colour temperature under most circumstances even with the flash. However, if it does not, you might want to use one of the other presets instead. Two commonly-used WB settings for flash photography are:

Flash: Increases the warm tones in the image to compensate for the slightly cooler colour temperature of the flash. The resulting image should have colours close to what the eyes see. 
Daylight: The light from on-camera flashes is close to that of sunlight, so the "Daylight" setting should also be able to compensate for the colour tones of the flash. This preset adds less warmth to the image than "Flash".

The WB presets might not result in accurate colours if the colour temperature from the flash changes or varies, such as in the following conditions:

- When bounce flash is employed (due to the colour of the bounce surface)
- When a diffuser is attached to the external flash unit (due to the colour of the diffuser)
- Different flash output (colour temperature may vary; depends on the flash)
- Deterioration of the flash over time

To ensure the most accurate colours for your scene, it probably would be best to adjust the white balance manually by using Custom White Balance or White Balance Correction. 

 

To recap the basics of white balance, read:
Camera Basics #6: White Balance

For more details about how to adjust colours using white balance, refer to:
Bounce Flash Photography – Change Color Using White Balance Settings

You might also be interested in our series on cosplay photography lighting techniques:
Cosplay Photography Techniques (1): Lighting Gear
Cosplay Photography Techniques (2): Fundamentals of Lighting
Cosplay Photography Techniques (3): Examples of Different Lighting Setups
Cosplay Photography Techniques (4): How to Shoot with Coloured Light
Cosplay Photography Techniques (5): Add “Fairies” to Your Images Using Long Exposure

 

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