Leonardo da Vinci's Camera Obscura
One scientific concept that most intrigued Leonardo was optics, the science behind how the human eye works. In Leonardo's time, it was generally believed that the eye issued forth sight rays that would bounce off objects and then return to the eye, enabling the person to see.
Da Vinci had the idea that this was wrong, because it should take too long for such a ray to leave the eye, bounce off of something and then return to the eye.
To explain this suspicion, he used the example of the sun. He said the sun was so far away that should a person need to send forth sight rays to see it, it would most certainly take a month before they could return.
The fact is, this estimate on the sun's distance from the earth was pretty far off. Da Vinci believed it was 4,000 miles away. In reality, it’s 93 million miles away.
Leonardo came up with a way to dissect eyeballs: he boiled them in water until the whites hardened, then sliced them open.
Da Vinci and the Human Eye
Leonardo thought of the human eye as the most important organ in the body. In his diary, he wrote, “This is the eye, the chief and leader of all others,” and used up hundreds of pages jotting down ideas about how the eye functioned.
He went so far as to dissect human eyes to study them. He used his observations to develop a projector, bifocals, and even came up with the idea for contact lenses - even though he never actually made them.
Leonardo also conceived of a gigantic lens to harness solar energy for the dyeing and tanning industry. Today, historians even believe that he came up with the idea of a telescope long before Hans Lippershey, the Dutchman who is credited with inventing the telescope in 1608.
Leonardo wrote, “...in order to observe the nature of the planets, open the roof and bring the image of a single planet onto the base of a concave mirror. The image of the planet reflected by the base will show the surface of the planet much magnified.”
The First Photographs - Joseph Nicephore Niepce 1827
In spite of being called a camera, a camera obscura isn't really the kind of camera we know today - it has no ability to take a photo that we can put in a frame. The first real photos were taken by a French chemist called Joseph Nicephore Niepce in 1827. Niepce set up a camera obscura and placed a polished pewter plate coated with a kind of asphalt called bitumen of Judea in it.
After 8 hours, Niepce cleaned the plate with a mixture of white petroleum and lavender oil, which dissolved away the parts of the bitumen that had not been hardened by light. The outcome was the very first photograph in history. Obviously, Niepce couldn't take images of people, as the only way to capture an image was by leaving the pewter plate to sit in the sun for hours and hours.
How Leonardo's Camera Obscura Worked
The camera obscura was one of the most interesting optical inventions Leonardo worked with. He was not the first person to use one of these, but he was first to notice the similarity between the way a camera obscura worked and the way the human eye functioned.
A camera obscura is merely a dark box (or even a very dark room) with a very small hole in one wall that lets in light. Directly across from the hole the image from the outside world will be projected onto the wall upside down.
The reason this happens is that light travels in a straight line, but when some of the rays reflected from a bright subject pass through a small hole, they become distorted and end up as an upside-down image. Imagine trying to squeeze an object into a space that is too small for it.
How The Human Eye Works
Da Vinci noticed that this is exactly the way the human eye sees things: light reflects off the surface of the object you are looking at and travels through a small opening on the surface of the eye (your pupil), and the image ends up flipped upside down.
He wrote, “No image, even of the smallest object, enters the eye without being turned upside down.” But he couldn't seem to figure out how a human eye actually sees the image right-side up. He didn't know what we know, that the eye’s optic nerve transmits the image to the brain, which then flips it right-side up. So the only thing the camera obscura lacks is a brain to flip the image!