Posts: 1
Joined: Fri Dec 30, 2005 11:55 am

photography experiment

Postby mwlicht93 » Fri Dec 30, 2005 12:00 pm

my science teacher gave me bad information please help!!
PLease help me!!

Former Expert
Posts: 4
Joined: Wed Dec 21, 2005 12:51 pm

Postby kan99 » Fri Dec 30, 2005 3:23 pm

Hello mwlicht93,
Here is an intense explanation of red eye/ why it occurs. I got it from a site I read.
The site says this:
The red eye effect is the appearance of red eyes on photographs taken with a flash. The light of the flash occurs too fast for the iris of the eye to close the pupil. The flash then illuminates the blood-rich retina at the back of the eye, resulting in red eye. The effect is generally more pronounced in people with gray or blue eyes and in children (larger pupils and less pigmentation than adults).

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, or green eyes in flash photographs.

Red eye can be prevented by increasing ambient lighting or by placing the flash away from the camera. Many modern cameras precede the flash by a period of bright light, allowing the iris to close ("anti red eye system"). Professional photographers prefer the former, as the anti red eye system does not always work (for example if people look away during the pre-flash).

If photos or videos are shot with infrared-sensitive equipment, the eyes also usually look unnaturally bright. The reason is the same: the blood-rich retina.

This is also very useful for you.
What causes red-eye and how do I minimize it?
Red-eye is caused by light from your flash bouncing off of your subject's retina. So, how do you minimize it? There are several approaches:

Minimize the subject's pupil size, thus reducing the amount of light that reaches the retina to be reflected back. The so-called red-eye reduction modes in many flashes and cameras today try to do precisely this by hitting the subject with a "pre-flash" of bright light designed to make the pupils constrict. The effectiveness of these methods varies quite a bit. The method of twinkling the flash rapidly for a second or two seems to be most effective - if it doesn't cause seizures in your subjects. Some cameras try to reduce pupil size by simply blinking a small bright light. This does not appear to be as effective as the twinkling flash method. Another less obvious tip is to avoid situations where pupils are likely to be dilated: Try to have people look into light and avoid taking pictures of drunk or otherwise impaired people.
Increase the angle from which the flash light is hitting the subject. Remember physics? Angle of incidence equals angle of reflection. If your flash is very close to your lens, the full intensity of the flash light will bounce off the subject's retina and come straight back into the lens. You can increase the angle by moving closer to the subject (though see notes above about portrait photography) or using an external flash, which moves the light source further from your lens. (Note that an unfortunate consequence of all of this is that those nifty, tiny little pocket cameras are the worst performers when it comes to red-eye. Their flashes have to be close to the lens because the camera is so small and they typically don't accept external flashes.)
Diffuse the light hitting the subject. The typical way to do this is to use an external bounce flash and bounce the flash light off the ceiling. This has the effect of illuminating the entire scene, rather than hitting the subject with a burst of intense light. It tends to reduce harsh shadows too. If you don't have a bounce flash, you can try attaching a diffuser to your existing flash or coming up with an ad hoc diffuser. Be careful with ad hoc diffusers: If they reflect light back into the flash, they can cause overheating and damage your flash.

Thanks for the question. If you need more info here are a few sites.

Good Luck with the experiment!
Thanks for the question, and I am glad to have helped you.

Return to “Preparing for the Science Fair”