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Treebeard's Stumper Answer
5 March 1999

Shoot My Own Feet

It was hard being a photographer at Disneyland last week. We spent a lot of time waiting in lines, and many rides are dark. I tried to get some action shots on the Matterhorn ride, a roller coaster that is out in the open part of the time. I had to let go of the safety bar to hold my camera, so I was jerked around a lot as I tried to snap pictures of the kids. I wasn't expecting much. I was surprised to discover that I took five pictures of my feet, and not a single shot of the kids or the sky! I wasn't trying to do this. Why did I only manage to shoot my own feet?

My feet on the Matterhorn
One of my better pictures from the Matterhorn ride.

I think I only shot pictures of my feet on the Matterhorn ride at Disneyland because of mass and inertia. The more massive an object is, the more it resists changes in motion. When the coaster car goes over a bump (but not a dip), and my finger is poised over the camera's shutter release button, everything is forced upwards. This accelerates my less massive camera against my more massive hand, which pushes the button. This also rotates the camera forward because the button is on the front edge of my camera. It's Newton's laws at work!


I think dips and bumps are different. When the car drops into a dip, my more massive body tends to hang in the air because of inertia. This does not push my hand against the camera, so I do not get unintended sky pictures in the same way I shoot my feet on the upward bumps. That moment of hang time would be the right time to take a picture.

When I read this answer to the kids at school, our director Ben gave me a "Treebeard, you're just too dang old to be riding roller coasters without hanging on!" look. I think Graybear agrees, but was too polite to say it:

My guess is that you had an automatically winding camera with only five pictures left on the roll. While concentrating on your grip on the coaster, you accidentally pressed the shutter button long enough to use up the film. When you tried to take the pictures, the ride was too noisy and bumpy for you to see the film was finished.

What I guess I'm saying is, "I'm stumped!"

I videotaped myself and my son on a couple of rides at last year's carnival - maybe Walt Disney can use the footage in one of their virtual rides. $;-)

That was a good guess about the motor drive, but it's not so. I was using my Olympus 320L digital camera, and I pushed the button for each picture. With this camera, I have to press the shutter button half way down to focus the camera, so my hand was always on the button. I shot my feet or the back of the seat every time. I stand by my stumper and answer.

more pictures
More pictures from Disneyland rides.

It's probably relevant that the Matterhorn ride does not have big drops and hills like a classic roller coaster. Like most rides at Disneyland where space is tight, the ride is designed with lots of tight turns and jerky bumps. A real roller coaster gives a smoother ride, so it would be easier to anticipate the hills and compensate when taking pictures. Video would also be easier to shoot than stills because there would be time to reposition the camera after each bump. The camera swings would make the video more exciting.

I remember seeing a documentary about the making of the second Indiana Jones and the Temple of Doom movie which features an exciting roller coaster-like chase in mine cars through burning tunnels. The ILM team first filmed the scene frame by frame using a modified 35mm still camera mounted on a model car in a miniature set. It looked too static, so they filmed real roller coaster rides to see what was missing. They found that the way a hand held camera swings up or down from the track is crucial for a realistic film, so they had to incorporate these swings in their animation.

It would be easier to do science at Disneyland if the lines were shorter. As it is, it's a long wait to test a hypothesis. I am getting too old for that!

Here are a few Web links about inertia for further study:

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