Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: neilep on 20/09/2006 20:00:53
-
Why do some people have red-eyes in photos ?...my daughter is one of them...and why only some people not all ?...are they possessed ?
I gather it has something to do with the retina !
Thanks
Men are the same as women, just inside out !
-
Well the clearer the eye the more light will reflect back out, children had fresher and clearer eyes, the fluid is at its best when you are young.
What you do speaks so loudly that I cannot hear what you say. (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activity4life.com%2Fphoto%2Fsheepbouncing.gif+&hash=159acaa741febc5b65a3b1d93c7395d2)
-
Well the clearer the eye the more light will reflect back out, children had fresher and clearer eyes, the fluid is at its best when you are young.
What you do speaks so loudly that I cannot hear what you say. (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activity4life.com%2Fphoto%2Fsheepbouncing.gif+&hash=159acaa741febc5b65a3b1d93c7395d2)
-
i dont think it has as much to do with particular eyes as much as particular light conditions and flash settings.
-
Yes, particular light conditions because the less environmental light, the more open are pupils, the more light enters the eye and is reflected by the retina (the red colour is because of blood in the retina). Some cameras, to reduce red-eye effect, send a first flash in order to close the person's pupil, and then, after some moments, the second flash for the photo.
Also, it depends at exactly wich angle the light from the flash hits the person's eye.
-
quote:
Originally posted by lightarrow
Yes, particular light conditions because the less environmental light, the more open are pupils, the more light enters the eye and is reflected by the retina (the red colour is because of blood in the retina). Some cameras, to reduce red-eye effect, send a first flash in order to close the person's pupil, and then, after some moments, the second flash for the photo.
Also, it depends at exactly wich angle the light from the flash hits the person's eye.
Ok perhaps I was assuming that it is taken the wider the iris the more light can reflect back. That why some systems have a pre flash to cause the eyes to react and reduce the iris size.
I have being taking pictures professionally now for some 30 odd years and in fact I began to learning black and white photography in school as we had a dark room and camera club. So experience has taught me that children are a lot more prone to red eye then adults. They also have far more clear crisp eyes along with the fact that they can open there iris fully unlike us old foggys I believe the this clarity also plays a part. Putting Vaseline over glass refracts and reduces the light as do impurities in water.
Here is one official bit of info I have come across
http://en.wikipedia.org/wiki/Red-eye_effect
Causes of red-eye
The light of the flash occurs too fast for the iris of the eye to close the pupil. The flash light is focused by the lens of the eye onto the blood-rich retina at the back of the eye and the image of the illuminated retina is again focused by the lens of the eye back to the camera resulting in a red appearance of the eye on the photo. (This principle is used in the ophthalmoscope, a device designed to examine the retina.)
The effect is generally more pronounced in people with grey or blue eyes and in children. This is because pale irises have less melanin in them and so allow more light to pass through to the retina. Children, despite superficial appearances, do not have larger pupils but their pupils are more reactive to light and are able to open to the fullest extent in low light conditions. Many adults have lost the ability to fully open their pupils except through the use of drugs.
In many species the tapetum lucidum, a light-reflecting layer behind the retina that improves night vision, intensifies this effect. This leads to variations in the colour of the reflected light from species to species. Cats, for example, display blue, yellow, pink, or green eyes in flash photographs.
What you do speaks so loudly that I cannot hear what you say. (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activity4life.com%2Fphoto%2Fsheepbouncing.gif+&hash=159acaa741febc5b65a3b1d93c7395d2)
-
That is very interesting, I always thought it was the angle of the camera and the lighting in the room!! Cool thanks!
I have no clue how pictures work even though I have had it explained a million times it facinates me, how the images are even printed and caught on the film.. I know its about light transfering image back to the film, but I don't get it! The red eye information I sort of understand! your eyes must work in a similar manner. Light reflecting image back into brain (or film in this case) leaving an impression there, where the brain takes over and remembers the image. I don't know what kind of an analogy that is but, that's what I would imagine!
Karen
-
HADRIAN...THANK YOU, also thanks to Gecko & Alberto for your valuable contributions also.
My family all have blue eyes, I always have to use red eye removal in a photo package....I'd much rather use that than use the red eye removal facility on the camera which takes time and usually always has me missing the moment....especially with the kids.
....ooops.....forgot to thank Karen Mam also..sorry !!...now how on earth did i manage to miss thanking you ?
Men are the same as women, just inside out !
-
Sometimes you are awefully silly, i was just reading along with everyone else... interesting really!
Karen
-
quote:
Originally posted by Karen W.
Sometimes you are awefully silly, i was just reading along with everyone else... interesting really!
Karen
Hi Kids in Karen Mams class.
Please give Karen Mam a big hug
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fhome.hccnet.nl%2Fenny.runkat%2Fzweyecat.gif&hash=8c95491fe4e5a1fd486553fb906327cb)
Men are the same as women, just inside out !
-
YAAAY I Got back on.....Forum was kicking my behind... OH NEIL SIR! How did you know I needed a hug???? So cute Has those sweet eyes like a scolded puppy ... nice hug Sir thanks....!! HUGS BACK TO YOU, I'd send you a graphic hug, but I don't know how.... HUUUUUUUUUUUGGGGGGGSS Back at you!![:X]
Karen
-
quote:
Originally posted by Karen W.
That is very interesting, I always thought it was the angle of the camera and the lighting in the room!! Cool thanks!
That certainly is a factor, and probably a more significant factor. If the flash unit (and it is usually something as powerful as a flash unit that causes it) is too close to the lens, you will get red-eye. If the flash unit is further away from the camera lens, the light bounced straight back out of the iris towards the light source will not be also heading towards the lens.
George
-
You mean to tell me I just got that sort of right!!!!! YAAAY... 1rt time for everything!
Karen
-
The answer to this is down to the size of the pupil and the rich blood supply of the retina.
When it's dark, our pupil opens up to admit more light into the eye so we can see. Photographers do the same thing and open up the aperture of their camera lens. But they also boost the available light, to make the colours look "natural", by using a flash.
So when you pose for a photograph and the flash goes off it illuminates the inside of the eyeball because the open pupil lets in lots of light. Since the back of the eye is a dense network of blood vessels, called the choroid, which supplies the retina, this glows up red and is picked up by the camera.
So how do red-eye reductions work? The camera sends an initial flash of bright light which causes the pupil to constrict, and then the photo (accompanied by the main illuminating "flash") is taken. This time the pupil is much smaller so much less light enters the eyeball to illuminate the choroid. As a result the eye looks black in the shot.
Why doesn't the pupil constrict in the first place? Because it takes over a fifth of a second for the eye to respond and close the pupil after a bright light is shone onto the eye. As a result the camera has already taken the picture by the time your eye thinks about closing its pupil!
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
If your flash photos (of humans) have "white-eye" rather than "red-eye",
the subject should visit the doctor immediately:-
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi24.photobucket.com%2Falbums%2Fc23%2FSUEDONIM%2F10640home-warning-signs.jpg&hash=a3f09a6ae2f7a5bef84e18db99b4341a)
" A retinoblastoma tumor can usually be seen with a flashlight. It may first be noticed in flash photographs. Instead of the usual "red eye," the child's pupil will look white. "
http://www.cnn.com/HEALTH/library/DS/00786.html
-
Yes, but let's not alarm people here. Retinblastoma is (thankfully) rare, and the majority of cases are seen in babies.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx