Thursday, October 16, 2008

Moonlit Foliage

I'm still taking my morning photo of the house across the river, though as I said a couple days ago, there is a gap with a significant change in fall colors over last weekend. Anyway, with the just-past full moon tonight and with my new programmable timer for my XSi just arriving, I thought I would take a moonlit shot for comparison.

So here is this morning's image, followed by one taken just now at 10:30pm (click to enlarge). By my back-of-the-envelope calculation, the night picture has about 120,000 times the exposure (1/160sec@F/10 vs 180secs@F/5), and I had to adjust the brightness a little more to match them, so really the difference in brightness is about 200,000. By the way, it is very calm tonight, thus the river is truly mirror-like. There is also a bit of a mist over the river - there is a freeze warning tonight, and the water is likely much warmer than the air temperature.

Interestingly, while I could see well enough to aim the camera, I really couldn't detect the foliage colors by the moonlight, while the camera could quite readily. This is not because of some magical properties of the camera, but rather, an everyday demonstration of how the eye works under low light levels. While the daytime world is quite colorful to our eyes, at night, we tend to see in shades of grey. We have two types of light detectors in our eyes - rods and cones. The cones are the color sensors, and require a higher illumination levels than the black-and-white sensors, the rods. Thus under low light levels, we tend to see in black and white. Unfortunately, this leads to disappointment sometimes at star parties after people see the magnificent color images from big telescopes and expect to see the same through our scopes. All they see are fuzzy grey blobs. But the colors are there and with exposure, almost any camera can record them.

1 comment:

Tuguldur said...

now the changes are more obvious