The Human Eye : Our Very Own Supercamera

Starting with the definition from Wikipedia: 

The human eye is an organ that reacts to light and has several purposes. As a conscious sense organ, the mammalian eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including colour differentiation and the perception of depth. The human eye can distinguish about 10 million colours

Similar to the eyes of other mammals, the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock.

You might, now, ask how many megapixels a human eye has. Well even if you didn’t, here's the answer.

The average human retina has five million cone receptors. Since the cones are responsible for colour vision, you might suppose that this equals a five megapixel equivalent for the human eye. 

But there are also a hundred million rods that detect monochrome contrast, which plays an important role in the sharpness of the image you see. And even this 105MP is an underestimate because the eye is not a still camera. 

You have two eyes (no kidding!) and they continually flicker around to cover a much larger area than your field of view and the composite image is assembled in the brain - not unlike stitching together a panoramic photo. In good light, you can distinguish two fine lines if they are separate by at least 0.6 arc-minutes (0.01.Degrees).

This gives an equivalent pixel size of 0.3 arc-minutes. If you take a conservative 120 degrees as your horizontal field of view and 60 degrees in the vertical plane, this translates to 576 megapixels of available image data!

Curiously - as a counterpoint to this - most people cannot distinguish the difference in quality between a 300dpi and a 150dpi photo when printed at 6x4", when viewed at normal viewing distances.

So: although the human eye and brain when combined can resolve massive amounts of data, for imaging purposes, 150dpi output is more than enough to provide adequate data for us to accept the result as photographic quality. 

But don't forget that women have more cones and men have more rods - I kid you not. Therefore the ladies see colours brighter than gents but can't see as well when it gets dark.

Here are 101 astounding facts about the human eye. Some of them are really surprising!

Sources: +Wikipedia +Lenstore +Yahoo! 


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Greenhouse Gases Cross The 400 ppm Mark

For the first time ever, National Oceanic and Atmospheric Administation (NOAA) scientists measured the average concentration of atmospheric carbon dioxide at 400 parts per million in Mauna Loa, Hawaii.
"We have now crossed a dangerous line in the global build up of greenhouse gases. Greenhouse gas concentrations have moved from the pre-Industrial Revolution level that never exceeded 280 parts per million (ppm) to a new daily average of 400 ppm. Over a period of the last million years, CO2 never exceeded 280 ppm . The last time greenhouse gases reached 400 ppm was three million years ago. Put simply, humanity has now changed the chemistry of our atmosphere to replicate pre-historic levels -- a time when no humans existed." +Elizabeth May

Is TOO MUCH Oxygen Bad For You?

The lung is an (obviously) important respiration organ in human beings. The lungs, located on either side of the human chest, remove carbon dioxide (CO2) and bring oxygen (O2) to the blood. But it's actually a bit more complex than that. Within your lungs, oxygen binds to hemoglobin and the carbon dioxide is released. Carbon dioxide is also released from sodium bicarbonate dissolved in the blood of the pulmonary capillary. The concentration of carbon dioxide is high in the pulmonary capillary, so carbon dioxide leaves the blood and passes across the alveolar membrane into the air sac. This exchange of gases occurs rapidly (fractions of a second). The carbon dioxide then leaves the alveolus when you exhale and the oxygen-enriched blood returns to the heart.

Respiratory System - Human Lungs - LiveScience

So now, the big question. What happens if we breathe 100% Oxygen?
We breathe air that is 21 percent oxygen, and we require oxygen to live. So you might think that breathing 100 percent oxygen would be good for us -- but actually it can be harmful. So, the short answer is, pure oxygen is generally bad, and sometimes toxic. +Marshall Brain  
 Read more about it at: - 100% Oxygen