What Causes Red Eye?
The topic of the cause of red-eye when taking flash photographs came up last night at a bridal shower slash barbecue. My explanation was that the light from the flash was reflecting off the back of the retina. Red-eye is more prevalent at night when the eye’s iris is widest open to let in the most light. Those annoying multi-flash, red-eye-reducing cameras attempt to fool the eye into thinking that there’s an abundance of light and to subsequently close the iris.
Well, I was pretty close, although it makes me feel a bit like Cliff Claven when I get these things even slightly wrong. No, it’s not technically the iris that opens and closes. Apparently I forgot some of my basic physiology. The iris is the colored part of the eye, the muscles that surround the pupil. Yes, the iris is just one of the body’s sphincter muscles; it opens and closes the pupil. “My, what a nice pair of sphincters you have!” Not an opening line you’re likely to hear often.
So, why red? I couldn’t remember at the time, but if you remember what’s back there in the retina you can easily figure it out: rods, cones, and blood vessels. The light is reflecting off the blood vessels in the retina right back to the camera. And since everyone I know has red blood, well, you “get the picture”…
The simplest methods to prevent red-eye? Use an off-camera flash. When the flash is too close to the lens, as on most point-and-shoot cameras, you get that lovely red demon-like reflection. The second best method? My favorite is Adobe Photoshop. Doesn’t prevent it, but it can remove the redness perfectly.
So what color is the reflection in the Queen Mum’s eyes?
if it is blood vessels reflecvting that cause red-eye… then explain why a dog or cat will have ‘green-eye’. You’re wrong again.
You’re also wrong about a lot of things that i cant even be bothered to point out.
A Canon G4 doesnt make you a photographer. A photgrapher has a real camera and not a point and squirt.
You’re blog sucks, who gives a fûçk on a lampost about your life? Are you so arrogant to assume they do?
Regards,
Sir. Matthew of Wembly
1. The epithelium or retina in many animals (including dogs, cats, and deer) have a special reflective layer called the tapetum lucidum that acts almost like a mirror at the backs of their eyes. Consisting of a compound called guanine, it reflects light outward and thereby allows a second chance for its absorption by visual pigments at very low light intensities. The visual pigments present in the eyes of these animals produce the non-red eyeshines of nocturnal animals. Humans, of course, do not have this tapetum lucidum layer in their retinas — therefore, the reflection off the retina shows the red color from blood vessels. Basic biology.
2. Partially agreed. Owning a Canon G4 would not make you a photographer, especially since there is no such thing. A camera allows you to be a photographer. But no specific model, make, or body style will make you a good photographer. That comes from knowledge, experience, and ability — things no camera manufacturer can provide. I can take great pictures with my Canon 30D or my Nikon F4 (both of which you would probably describe as real cameras), but I can also take great pictures with my Canon G3 “point and squirt”. My credentials include serving several years as a photojournalist for a domestic news agency in Washington DC, and having commissioned photographs published in several worldwide magazines. Yours, Sir Anonymous?
3. Perhaps. But, I am not so arrogant that I would come to your website, make comments on a topic of which I am obviously uninformed, and repeatedly fail to belittle you at the same time. At least try to form one sentence that doesn’t have spelling or grammatical mistakes. Thanks for visiting.
In my experience, when someone “cant even be bothered to point out” examples of the things they are complaining about it’s because they don’t have any.