Monday, July 16, 2012

Matching dappled light to projecting leaves

On a recent sunny day, I noticed this pattern of light and shadow cast across a road. The shadow looked like a piece of dark paper with holes punched out of it.

The circles of dappled light were about three inches in diameter, and they were all of constant size. However some circles were brighter than others.

I looked up to see what was casting the shadow. It was a maple branch 18 feet above the ground. The branch presented a fairly flat projecting surface with a fixed distance from the ground. This is why the circles were the same size.

Typically a tree or a forest presents a variety projecting of surfaces positioned at many different distances from the ground, so the circles or ellipses vary in size and focus. The farther from the ground, the larger—and blurrier—the circles.

I wondered if I could match up the projecting surface of leaves with the pattern on the ground.

It's a pretty close fit, but doesn't match exactly because they aren't shot at exactly opposite angles. At the bottom of the photo on the right you can see the sharp cast shadow of my arms holding up the camera.

Anyway, it's clear that every opening in the leafy surface, regardless of its size or its ragged shape, has its corresponding circle or composite blob of light on the ground.

The branches aren't thick enough to block the sun from that distance, so they disappear completely in the shadow.

Previously on GJ: Dappled light

Bob Mrotek said...

Actually, the circles made on the ground are copies of the sun. the gaps in the leaves no matter what the shape are lenses make for a round "camera obscura" effect.

James Gurney said...

Yes, Bob, exactly, thanks for mentioning that. They're essential pinhole projections of the disk of the sun, even though the spaces are a lot bigger than pinholes. On partial eclipses, the circles have a corresponding shape.

Rich said...

I always like to observe negative spaceings. This lesson here has got an additional "sun-touch";-)

Guess leaves' shadows under artificial light would offer a different pattern.

courtartist said...

....and during an eclipse bright crescents are projected between the shadows of leaves.

jill polsby said...

I love your casual way of showing, teaching...thanks for this wonderful observation of shadows. And then, too, thank you to the commenters for making the lesson even more interesting.

etc, etc said...

Shouldn't one of the side-by-side images be flipped horizontally for a more acurate comparison?

James Gurney said...

Etc. Yes, of course, you're right. I wasn't thinking. One of them should be flipped horizontally. Now they're sort of mirror images of each other.

Jesse said...

Thanks for this post. I had a great time yesterday looking up at the trees, down at the shadow. Sort of like watching a tennis match.