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View Full Version : What causes redeye?



JohnBrowning
08-10-2004, 09:02 AM
Is it the size (power) of the flash? Is it the location of the flash in relation to the lens? Something else?

Rhys
08-10-2004, 09:12 AM
Is it the size (power) of the flash? Is it the location of the flash in relation to the lens? Something else?

It's all of the above.

What happens with red-eye is that the light from the flash is reflected back towards the flash from the red blood cells in the eye. Those with darker eyes don't get this as the colour's dark enough to mask the light. Because blue is such a weak colour, the light penetrates and reflects off the blood vessels. Moving the flash away from the lens axis reduces this problem greatly. Causing the subject to reduce the size of his/her pupils also helps a lot - hence the anti-redeye pre-flash on many cameras. The power of the flash also plays a part.