Problem – Red eye effect

Another notorious problem that occurs in flash photography is the „red eye effect“. This problem mainly occurs with built-in flashes where the distance between flash reflector and lens is very short. What is the cause of this phenomenon? The human eye adjusts to light with the help of its pupil. If the light dims, the pupils widen. When capturing a person using a flash, the light reflects off the retina and appears as a red dot in the picture. The further the flash is from the lens i.e. the wider the angle between lens, eyes and flash is, the less red eye effect problems occur. 

Most modern cameras have a built-in red eye reduction.  Usually a pre-flash or an additional light dazzles the person. By dazzling the person, the pupil’s size should be reduced, reducing the risk of red eye. However, this only works if the person is close to the camera and is looking at the source of light head on. This form of red eye reduction correlates with a time delay between triggering the shutter release and exposure. Often subjects turn away from the camera thinking the shot was already taken. This form of delay is frequently mistaken for the much discussed shutter lag. However, the method mentioned above is not a technical defect; it is simply a delay that the eye needs in order to react accordingly to the light.

While in analog photography correcting red eye can be relatively time consuming (for this purpose there are e.g. special correction pens), correcting images from digital photography is unproblematic. Nearly every image editing program provides tools for this purpose.

Tip
If image post-processing is acceptable, the red eye reduction on digital cameras can be deactivated. The camera’s speed for flash images is then considerably higher.

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