red eye

[waboo]

what causes red eye and how can I eliminate it if I can.

 

[tempra]

it's a reflection from the back of the eye caused by your flash.

Ways to eliminate it are to use an external flash so it's not in direct line with the eye and the lens, don;t use the flash, fire a pre-flash which makes the iris in the eye close and reduce the light bouncing back out of it, use PS to clone it out.

There's probably a few other good tips around as well

 

[fadingaway1986]

Basically you get red eye at night or when the photo is taken in a dark place.
When you are in a dark situation - your iris opens up (I assume to allow more light in so you can see), the back wall of the iris is red - so like all other colours - when the flash hits it - the red is illuminated and reflects back into the camera...

I dunno if that is exactly correct - but gee I feel smart! (I am sure my theory is very close to correct, maybe a few incorrect terms or explanations).

So basically in order to avoid it - you need have the flash so it is not pointing into their eyes - therefore the light would not be shining at the back wall of their iris - and you wouldn't get any flash...

OR - you could carry around those cool torches Mulder and Scully have and shine them in everyones eyes for a while before you take the photo - hence tricking the iris into thinking its light again - and it will close... (Or you could just use the red-eye feature a lot of cameras have. But I believe it would not be as effective... Or as fun!)

i think its time for me to go to bed now.

 

[Hertz van Rental]

the back wall of the iris is red - so like all other colours - when the flash hits it - the red is illuminated and reflects back into the camera...

What you meant to say is that the light bounces of the back wall of the eye - which is the retina (not the iris).
I'm still investigating why it is red. I don't think it is anything to do with the capilaries in the retina, because this would not account for why some animals' eyes reflect blue and even green.
I used to have a cat that had one blue iris and one green. If you photographed her with flash one glowed green the other red.
I have found no explanation - or even research - on this effect but I'm still looking.

My guess was wrong and you learn something new every day. Nocturnal animals have a reflective layer to increase light absorption - which is why their eyes reflect a different colour. So it is the capillaries in the retina that cuase red-eye*
http://science.howstuffworks.com/question51.htm

*Maybe I should have edited this so I looked cool and knowledgeable :lmao:

 

[fadingaway1986]

Yeah well, I failed science. Never did biology. But my THEORY was correct.

 

[Hertz van Rental]

Quite so. And it will teach me to try to answer questions off the top of my head when I'm tired ;-)