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Author Topic: What causes red eyes in photographs?  (Read 8310 times)

Offline laird rob

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What causes red eyes in photographs?
« on: 06/12/2009 20:30:02 »
Rob Waite  asked the Naked Scientists:
   
Hi Guys,
  
Can I first start by thanking you all for such newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive], I have all my family hooked and we can hardly wait each week for the next addition of the newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive] to be released.
  
I have a question about "redeye" when taking a picture using a camera. I've recently started the task of correctly sorting through all by digital pictures on the computer. I have noticed that in some of my pictures people have red eyes.
  
I've read somewhere before that this is due to light reflecting back out of the eye, but in the case of my photographs, it only seems to be certain members of my family who have red eyes. I myself NEVER have red eyes on photos, but my wife often does.
  
This is especially strange in family photographs when I am the only one who doesn't get the red eye effect.
  
Just wondering if you could explain what redeye is, are there any tips to avoid redeye when taking picture, and why some people are more prone to others to having redeye.
  
Thanks, newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive],
  
Rob (in Leeds)

What do you think?


 

Offline Bored chemist

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What causes red eyes in photographs?
« Reply #1 on: 07/12/2009 19:57:07 »
One possible factor is that the light won't be focussed and reflected back properly if you are short or long sighted to a significant extent.
Also, if you (for whatever reason) don't look straight at the camera then you don't get red-eye.
 

Offline Geezer

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What causes red eyes in photographs?
« Reply #2 on: 08/12/2009 03:19:52 »
I believe the red colouration is caused by the blood vessels in the retina.

BTW, if your eyes don't show red in flash photographs, you might want to check that you do actually cast a shadow during daylight. I believe the two effects are related.

(OK - The second bit is baloney, but I think the first part is true.)
 

Offline laird rob

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What causes red eyes in photographs?
« Reply #3 on: 08/12/2009 18:11:31 »
Hello, just to let you know, my eye sight has always been really good. I've recently had my eyes tested and no problems in "sightedness" have been found.

Come to think of... another question - How does the "redeye reduction" feature work on cameras?

It's all very strange.
 

Offline thedoc

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Offline Chemistry4me

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What causes red eyes in photographs?
« Reply #5 on: 08/12/2009 21:03:48 »
How does the "redeye reduction" feature work on cameras?
A number of low powered flashes or a really bright flash will occur before the main flash, causing the iris to contract.
 

Offline techmind

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What causes red eyes in photographs?
« Reply #6 on: 10/12/2009 22:12:48 »
How does the "redeye reduction" feature work on cameras?
A number of low powered flashes or a really bright flash will occur before the main flash, causing the iris to contract.

That's the traditional way.

Some modern digital cameras use an image-processing technique to automatically/algorithmically 'paint out' redeye. Unfortunately the method is not foolproof, and can sometimes result in blacked out teeth and other such artifacts!
 

Mani

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« Reply #7 on: 09/01/2013 08:31:41 »
Since the red eye effect is due to the light reflecting back from a persons eye, i think a person being short sighted has more chance of showing a red eye. The logic being, that a short sighted person without his/her glasses/contact lenses would have a dilated pupil while trying to focus on the camera. This will result more light getting out of the eye and hence more prone to this effect.
 

Tanya

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« Reply #8 on: 07/06/2013 19:31:13 »
I have a question regarding red eye in photographs. I was recently in the Amazon and was told by our guide that when we shine the light on different animals the nocturnal ones will reflect back red eyes and the diurnal animals reflect back green. Is this true? If so, why green? And then shouldn't humans reflect green?
 

Offline RD

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Re: What causes red eyes in photographs?
« Reply #9 on: 07/06/2013 20:31:01 »
... I was recently in the Amazon and was told by our guide that when we shine the light on different animals the nocturnal ones will reflect back red eyes and the diurnal animals reflect back green. Is this true?

Eyeshine any colour other than red is tapetum lucidum used to improve night vision.
However a red reflection can still be a nocturnal animal.
« Last Edit: 08/06/2013 13:00:12 by RD »
 

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Re: What causes red eyes in photographs?
« Reply #9 on: 07/06/2013 20:31:01 »

 

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