Just had the most interesting discussion with Kavin because he asked me what the resolution of the eye is.
I told him that the eye is a sphere. So its resolution should not be expressed in terms of 2D measures such as 4K or 8K. A good eye has the angular resolution - the power to "resolve" two objects - that are an arcminute apart - roughly 0.02° apart.
And so we looked at a printer sitting far away and how much detail on it we could pick up. But if the printer was brought very close to us, it would easily cover 45° of our field of vision, and we could easily see spectacular detail on it, such as specs of dust.
At a distance of a kilometer, an arcminute translates to 0.3m. Which means I could easily count the number of participants in a human chain a kilometer away. There is no limit to the range of view of the human eye - we can see stars that are thousands of light years away. If it weren't for the dust and heat in the atmosphere, we could theoretically see till infinity (as long as there was a bright enough object over there). I wonder what astronauts see when they look out of their spacecraft windows.
I then came across this wikipedia article, and it is simply marvellous how much power the eye possesses. The field of view of the eye is approximately a cone with a width of 175° and a height of 160° - that's almost a hemisphere. To be fair, we can only read or recognise faces in a cone at the center of our eye with an angle of 6 or 7°. But the rest of our peripheral vision can also do spectacular things - like alert us about an approaching threat.
We can identify some pretty faint stuff. We can see between 5,600 and 45,000 stars in the night sky, which explains why I was stupefied as I stepped out of my tent last summer near Chitkul. In the city this number drops to only 50 stars. You can also see about 5 planets without a telescope, as well as the ISS and other man made objects. Before the telescope was invented, Tyco Brahe went about charting the entire night sky using just his eye. Not to forget, civilizations before him charted and predicted eclipses to within minutes using just the naked eye for observation.
And then comes the really interesting stuff - what the eye does in combination with the visual cortex, continually and subconsciously. You know the size and position of all objects around you, in 3D space, as well as their motion. You're calculating vectors in your brain all the time. You know if something is vertically and horizontally aligned or not - and as Kavin observed, you know that even if your head is itself tilted at an angle.
And finally, you can tell apart subtle changes in the luminosity and shades/colours of an object. We spent a lot of time staring at a multicoloured fairy light. Indeed, we can tell the period of glow of each light, and when a light glows brighter than it was glowing before, or changes colour. Amazing.
Kavin feels that this constant processing of our vision by our brain is an unnecessary drain on our energy reserves, especially now that we no longer live in hostile environments. "Those jars of dry fruits aren't going to jump out of the almirah and attack me, so why is my brain constantly assessing their motion when I'm basically just staring into infinity and thinking of something else". That makes sense. Which is why it's a good idea to shut our eyes when tired, sick or malnourished - it (hopefully) turns off the GPU coprocessor in our brain constantly crunching inputs from 126 million rod and cone cells.
Any other fascinating facts that you know about our eyes and vision system?
I told him that the eye is a sphere. So its resolution should not be expressed in terms of 2D measures such as 4K or 8K. A good eye has the angular resolution - the power to "resolve" two objects - that are an arcminute apart - roughly 0.02° apart.
And so we looked at a printer sitting far away and how much detail on it we could pick up. But if the printer was brought very close to us, it would easily cover 45° of our field of vision, and we could easily see spectacular detail on it, such as specs of dust.
At a distance of a kilometer, an arcminute translates to 0.3m. Which means I could easily count the number of participants in a human chain a kilometer away. There is no limit to the range of view of the human eye - we can see stars that are thousands of light years away. If it weren't for the dust and heat in the atmosphere, we could theoretically see till infinity (as long as there was a bright enough object over there). I wonder what astronauts see when they look out of their spacecraft windows.
I then came across this wikipedia article, and it is simply marvellous how much power the eye possesses. The field of view of the eye is approximately a cone with a width of 175° and a height of 160° - that's almost a hemisphere. To be fair, we can only read or recognise faces in a cone at the center of our eye with an angle of 6 or 7°. But the rest of our peripheral vision can also do spectacular things - like alert us about an approaching threat.
We can identify some pretty faint stuff. We can see between 5,600 and 45,000 stars in the night sky, which explains why I was stupefied as I stepped out of my tent last summer near Chitkul. In the city this number drops to only 50 stars. You can also see about 5 planets without a telescope, as well as the ISS and other man made objects. Before the telescope was invented, Tyco Brahe went about charting the entire night sky using just his eye. Not to forget, civilizations before him charted and predicted eclipses to within minutes using just the naked eye for observation.
And then comes the really interesting stuff - what the eye does in combination with the visual cortex, continually and subconsciously. You know the size and position of all objects around you, in 3D space, as well as their motion. You're calculating vectors in your brain all the time. You know if something is vertically and horizontally aligned or not - and as Kavin observed, you know that even if your head is itself tilted at an angle.
And finally, you can tell apart subtle changes in the luminosity and shades/colours of an object. We spent a lot of time staring at a multicoloured fairy light. Indeed, we can tell the period of glow of each light, and when a light glows brighter than it was glowing before, or changes colour. Amazing.
Kavin feels that this constant processing of our vision by our brain is an unnecessary drain on our energy reserves, especially now that we no longer live in hostile environments. "Those jars of dry fruits aren't going to jump out of the almirah and attack me, so why is my brain constantly assessing their motion when I'm basically just staring into infinity and thinking of something else". That makes sense. Which is why it's a good idea to shut our eyes when tired, sick or malnourished - it (hopefully) turns off the GPU coprocessor in our brain constantly crunching inputs from 126 million rod and cone cells.
Any other fascinating facts that you know about our eyes and vision system?