Moon through the trees at Tiffany Falls
Last night I went to take pictures at Tiffany Falls. It’s close to home, it’s pretty, and it was a lovely night. My fingers and toes got cold after an hour or so, but otherwise, it was a wonderful experience.
This got me thinking about why things look different at night vs. during the day. After the cut, I’ll post a few more pics, where I try to explain my understanding of why night and day seem so different to us, light- and color-wise, even though the only really fundamental difference is brightness.
On the right is a photo of Tiffany Falls that I took last night.
This is kind of what it looked like in the moonlight, and this picture really was taken by moonlight (f/2.8 @ 30″, ISO 400). The way I made it look this way was by increasing the brightness and contrast, tinting the picture blue, then desaturating the picture almost completely (i.e., removing color).
Now, if you look on the left, this is how the photo came directly out of my camera. Looks like daytime, no? Kind of annoying, really. I’m trying to take this wonderful moonlit scene, and then it turns out looking like late afternoon, in full color.
At night, we see the world by moonlight (or starlight) as being nearly black and white in its shading. This is, I think, due to an optical illusion. It’s because of how our eyes work. It’s not because of the light; the light is nearly sunlight-colored. It’s sunlight reflected from the moon, and the moon is light gray. This means that the moon doesn’t change the color of the light it gives to us from the sun (not noticeably, at least); it just dims it down a bit (because it’s gray) and the overall amount of light is much, much less (because of the fact that it’s a very small surface to reflect light to us, vs. the sun, which is a very large surface, blasting all that light directly).
A few websites I found (you can google, yourself) say that the sun, from our perspective, is 400,000 times brighter than the moon1. So, night is not only darker than daytime, it’s a LOT LOT LOT darker than daytime. The fact that our eyes are capable of adjusting to that kind of difference is pretty phenomenal. They do this in several ways. First, the iris can contract or expand (exactly like a camera shutter) to let in more or less light, depending on conditions. Second, the retina (kind of like the “film” or CCD that receives light at the back of the eye) is sensitive to light levels, and the cells there can adjust their rate and intensity of messages being sent to the brain. Third, we have two kinds of light-sensitive cells in our eyes, and one kind works better in the dark.
Cones are our color-sensitive cells. We have 3 kinds (red, green and blue) and they are wired together in very clever ways. They are the reason we see color. They tease out the wavelength information from the light that enters our eye, and send it to the brain. The brain then shows us colors :). Cones require a lot of light to function, however.
Rods, on the other hand, require very little light to function (and they are wired together in different, also clever ways, to require even less light). They respond only to the intensity of light, not its wavelength; so, they see in black and white. Some animals only have rods (or something like them), so they cannot see color.
In very dim light, cones don’t work, so we don’t see color. The color is usually there, all around us (as in starlight or moonlight), but we can’t see it, because our cones have shut down (sort of), due to insufficient stimulation. The rods work pretty well in those conditions, though. So we see in (mostly) black and white.
The end.
This shot is just for fun. You can see how the stars are ovals, smeared from lower left to upper right in the photo. Even at 30 seconds, the stars moved that far across the sky (well, OK, I moved, but you get my meaning). In reality (as you may be able to see), the stars move in a circle–or semicircle–around the sky, leaving little curved streaks. I have pictures of that, somewhere…
1Photography bears this out, at least in general priciple. The picture I took of Tiffany Falls at night was with an aperture of f/2.8, an exposure time of 30 seconds, and an ISO “film speed” (not really; it was digital) of 400. This gives me roughly the same exposure as if I had used an aperture size of f/16, an exposure time of 1/500 of a second, and the same film speed. From f/16 to f/2.8 is 5 “stops”. Each “stop” means that we have either doubled or halved the amount of light on the film or CCD. So, opening the aperture 5 stops, we’ve increased the light by 2 X 2 X 2 X 2 X 2 (or, by 25). That means we have 32 times more light coming in, just from changing the aperture. But we’ve also changed the exposure time from 1/500 of a second to 30 seconds. This can be measured in “stops” as well (it turns out to be 215), or by using more direct math: 30 divided by 1/500 = 30/.002 = 15,000. So, we’ve made 15,000 times more light hit our film or CCD by increasing exposure time from 1/500s to 30s. But we changed both the aperture and the shutter speed, so we need to multiply them. 32 X 15,000 = 480,000. Pretty close to what the websites say. Given our fudge factor (there was one), it’s definitely within tolerance limits. Cameras are pretty cool. So are our eyes, because we don’t need 30 seconds of staring at something to see it at night, and within seconds (a lot of seconds, but still…) we can see things during broad daylight, too, without going blind.
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