Una goccia d'acqua colorata (A single colorful droplet)
May a crystal clear drop of water be colorful? The answer is yes! Rainbow is the proof. But looking at the rainbow we never realize that those wonderful set of colors comes from single drops. Each drop is seen with different angles and this difference is the color. Larger view angles make the drops red, smaller view angles make the drops blue. To better understand the phenomena have a look to the document I wrote some time ago and now reviewed. See this document.
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During the night some dew formed in the grass. The morning after, while I was walking, I noticed a small spot of colored light in the grass with the tail of my eyes. I stopped myself and I turned my head toward it. No mistakes: that was the rainbow light from a single droplet, red on one side and blue on the other! I run and stumbled into home looking for my camera. I went out trying to find back the position: it was extremely critical! As expected the angle through which I could see the colored drop was very small and the distance to the drop was only a couple of meters. But the spot was so bright! I took the camera and aimed it to the light source in the grass. What a disappointment! No spotlight in the camera! How was it possible! With my eye the light was clear and bright but with the camera, nothing! Then I noticed that I could see the light only with one eye at time. Now my guess is that the eye, with its small pupil, records the light from a very small angle while the camera, with a wide angle lens, collects the light from a wider angle and no colored spots appears. Only 1.74° separate the red ray from the blue ray. So to record the light I used a trick: blur the image, set it out of focus! Doing so, the angle of details cover a much larger area on the sensor: rays from small angles hit the sensor surface at larger distances and… the rainbow magically appeared. A rainbow from a single drop!
During the night some dew formed in the grass. The morning after, while I was walking, I noticed a small spot of colored light in the grass with the tail of my eyes. I stopped myself and I turned my head toward it. No mistakes: that was the rainbow light from a single droplet, red on one side and blue on the other! I run and stumbled into home looking for my camera. I went out trying to find back the position: it was extremely critical! As expected the angle through which I could see the colored drop was very small and the distance to the drop was only a couple of meters. But the spot was so bright! I took the camera and aimed it to the light source in the grass. What a disappointment! No spotlight in the camera! How was it possible! With my eye the light was clear and bright but with the camera, nothing! Then I noticed that I could see the light only with one eye at time. Now my guess is that the eye, with its small pupil, records the light from a very small angle while the camera, with a wide angle lens, collects the light from a wider angle and no colored spots appears. Only 1.74° separate the red ray from the blue ray. So to record the light I used a trick: blur the image, set it out of focus! Doing so, the angle of details cover a much larger area on the sensor: rays from small angles hit the sensor surface at larger distances and… the rainbow magically appeared. A rainbow from a single drop!
