Friday: 15 December 2006
This morning was very foggy, and so it afforded an initial photographic experiment in detecting the green laser pointer beam of a couple of days ago. It’s not as dramatic as I had hoped for - I think the batteries are low.
The fog allows us to see the beam in the first place - if it were very clear and dry there would be no hope. Being able to see the beam like this requires that the light be reflected at right angles - the tiny water droplets in the air accomplish this task for us. If it were dry, the camera wouldn’t see the green light because there wouldn’t be anything to reflect it toward the lens.
It’s a double-edged sword, though - as you can tell looking from left to right the intensity of the beam fades over the 4 meter length that you see here. And that’s because the fog is absorbing the light, as well as reflecting it.
(Just in case you might wonder, my eyes had no trouble seeing a very intense beam; it’s just that the camera doesn’t do such a great job of capturing the photons that strike my eyes with far greater effect than they do the CCD detector in the camera.)
And that provokes in me the much larger question of how we see color. Of course there’s rods and cones and all that stuff - but how do we tell something is green or blue or red? How do we explain the various sorts and grades of colorblindnesses? I won’t get into that explanation at the moment, but here’s an interesting experiment.
Here’s a field of colored and white squares.
Beginning with the red panel, stare at the cross in the center of the red field for 30 seconds, then flick your eyes to the adjoining white field at the right. (You might want to scroll so as to eliminate the lower green half from your field of vision.)
What color do you see, briefly, in the white field?
Now do the same for the lower half, whose left field is green. What color do you see in the white panel when you flick your eyes to the right?
You should see a green afterimage in the first instance of staring at red, and then a red afterimage in the second instance of staring at green.
Here’s another one, this time with blue and yellow. Again, the afterimage should be the opposing color. Staring at blue will not yield red or green, but only yellow, and so forth.
The color pair of red and green appears to be distinctly different and self-contained in its afterimage behavior from the pair of yellow and blue and its afterimages.
How interesting! And it turns out that there is a reason for this that has to do, not with complementary colors or anything silly like that, but at the most basic level the arrangement of three types of cone cells, how they interact with each other in order to detect these colors, and how they transmit the information on what color is being perceived to the brain. The afterimages tell the whole story.
More later, but anyone who already knows about this is welcome to explain!
The fog allows us to see the beam in the first place - if it were very clear and dry there would be no hope. Being able to see the beam like this requires that the light be reflected at right angles - the tiny water droplets in the air accomplish this task for us. If it were dry, the camera wouldn’t see the green light because there wouldn’t be anything to reflect it toward the lens.
It’s a double-edged sword, though - as you can tell looking from left to right the intensity of the beam fades over the 4 meter length that you see here. And that’s because the fog is absorbing the light, as well as reflecting it.
(Just in case you might wonder, my eyes had no trouble seeing a very intense beam; it’s just that the camera doesn’t do such a great job of capturing the photons that strike my eyes with far greater effect than they do the CCD detector in the camera.)
And that provokes in me the much larger question of how we see color. Of course there’s rods and cones and all that stuff - but how do we tell something is green or blue or red? How do we explain the various sorts and grades of colorblindnesses? I won’t get into that explanation at the moment, but here’s an interesting experiment.
Here’s a field of colored and white squares.
Beginning with the red panel, stare at the cross in the center of the red field for 30 seconds, then flick your eyes to the adjoining white field at the right. (You might want to scroll so as to eliminate the lower green half from your field of vision.)
What color do you see, briefly, in the white field?
Now do the same for the lower half, whose left field is green. What color do you see in the white panel when you flick your eyes to the right?
You should see a green afterimage in the first instance of staring at red, and then a red afterimage in the second instance of staring at green.
Here’s another one, this time with blue and yellow. Again, the afterimage should be the opposing color. Staring at blue will not yield red or green, but only yellow, and so forth.
The color pair of red and green appears to be distinctly different and self-contained in its afterimage behavior from the pair of yellow and blue and its afterimages.
How interesting! And it turns out that there is a reason for this that has to do, not with complementary colors or anything silly like that, but at the most basic level the arrangement of three types of cone cells, how they interact with each other in order to detect these colors, and how they transmit the information on what color is being perceived to the brain. The afterimages tell the whole story.
More later, but anyone who already knows about this is welcome to explain!
