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Pixel Engineering: Long Exposure Photography

7 minutes

(Describer) On an Etch-a-Sketch, rectangles spell MIT – Title: Massachusetts Institute of Technology.

Hey there. I'm Jeff. And I'm Steve. We're students at MIT. We're going to be showing you some cool things you can do with photography and science at home. Things like this.

(Describer) They step away from where they stood on a lawn in front of a building, and time moves in fast-motion, with the sky getting darker and lights turning on at the building. A match burns in slow motion, and Jeff holds something close to a camera lens.

Hey, first look.

(Describer) Other photos include a fly, a flower in a drop of water, a hammer shattering a light bulb and a dart exploding a balloon.

(Describer) Steve hops up and down wearing a Steadicam harness, then extends the arm that holds a camera.

It stays still. It's pretty cool like that. You can let it go.

(Describer) Other photos feature glowing squiggles and curves of light. In a film, a view of city lights at night is refocused to show each light has the MIT logo. The view turns to a white logo against a black background. More titles are added: Pixel Engineering at MIT. Long exposure photography. By an exhibit titled “Visionary Engineer, Harold Edgerton,” Jeff:

We're at the MIT Museum at the Doc Edgerton exhibit. Edgerton was a professor at MIT who pioneered the use of the stroboscope in photography to capture images like these.

(Describer) a bird taking off.

The strobe can be triggered to illuminate the subject for an instant, allowing the camera to capture a moment frozen in time. Today, instead of capturing an instant, we'll use long exposure photography to capture events as they take place over time. Let's go back to the lab and meet up with Steve.

(Describer) He holds up his forearms and bends down.


(Describer) Waves blur the image and he ends up in a lab with Steve.

Jeff, where's your lab coat? Oh, yeah, sorry.

(Describer) The waves blur again, then Jeff wears a lab coat like Steve wears.

[both trilling]

Now that we're in proper lab attire, let's look at our basic camera setup.

(Describer) On a table...

Here's our light source.

(Describer) one end.

This is our scene, which is at the focal distance of our lens.

(Describer) A magnifying glass.

Here's our aperture,

(Describer) A circle that opens.

our shutter,

(Describer) A door he lifts.

and our piece of film or digital sensor.

(Describer) A screen at the other end.

Let's take a closer look at, in this case, our sensor. Think of each square as representing a pixel, which cumulatively records light as it hits it.

(Describer) The screen is made up of little tiles.

If we open the aperture, we can see the image resolve on the sensor.

(Describer) A heart and the logo.

Changing the aperture size controls the amount of light hitting the sensor. Another way of controlling light is with the shutter. Because of the sensor's cumulative nature, opening the shutter for longer periods means each pixel records a higher light count, resulting in a brighter image. This is the key to long exposure photography. Another way to understand it is with an example. Here I am in a dark room, waving a flashlight around. This video is made up of successive photographs, or frames, played back to back at around 24 frames per second. If we superimpose all these photographs together, we get an approximation of a long exposure of the scene. This is due to the cumulative nature of the camera. Here's what the actual continuous long exposure of the scene looks like.

(Describer) He’s drawn a smiley face with light.

That's the basics. Now you can do this at home. First, you'll need a dark environment, a camera, a tripod or steady place for the camera, a light source, and it helps to have a happy assistant.

(Describer) Steve smiles and waves.

Secondly, you need to set your camera to a slow shutter speed, at least five seconds. If you have a digital SLR, use manual or bulb mode. You can set a compact camera to fireworks or night mode to trick the camera into taking a long exposure. Next, trigger the shutter and have your assistant wave a light to write words or draw shapes. After the shutter closes, you'll have your light painting.

(Describer) He’s drawn a math formula with light.

There are many uses for long exposure photography, both scientific and artistic. For example, you can measure the speed of an object, like a car or a plane.

(Describer) Light streaks across a sky.

Here we have a plane landing. If we know the distances and the time the shutter was open, we can calculate the plane's speed. You can see the parabolic trajectory of an object with a glow-in-the-dark bouncy ball.

(Describer) Steve drops one.

With long exposure, you can calculate the decay of bounces. The path of the ball is brighter at the top of the arcs because it is moving more slowly near the apex.

(Describer) More glowing curves stretch from where it bounced off a wall.

Another cool application is astrophotography. If you use stars as your light source, you can see the Earth's rotation. At the center of the rotation is the North Star. Finally, if you're at MIT and have access to a high-tech robotic arm, you can do precise light painting. Let's check it out.

(Describer) At another lab...

We're at the Mediated Matter Group at the MIT Media Lab. We're using this arm to do light painting.

(Describer) The arm moves up and down.

By attaching a light to the end of the robotic arm, we can actually create light paintings like this.

(Describer) A red and black MIT logo against a white background.

Because of the precise control of the arm, we can make animations where every video frame is its own light painting.

(Describer) A glowing cube grows and shrinks.

We can also visualize hidden fields by attaching a sensor and controlling the brightness of the light with the sensor. For instance, this is my laptop, and you can see the magnetic field surrounding it.

(Describer) Vertical red and yellow streaks that get shorter the further from the screen.

That arm was pretty cool. Definitely, but you don't need a robotic arm, just a flashlight and camera to try light painting. That's the end of our video. Hope you enjoyed it. This was our first try doing this. If you have any comments, suggestions, or want to share some photos, feel free to contact us at... This right here. This will work.

(Describer) Pixelengineering at

Thanks for watching.

(Describer) Titles: Pixel Engineering. Copyright MIT 2012. Accessibility provided by the U.S. Department of Education.

Accessibility provided by the U.S. Department of Education.

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Two MIT students discuss the relationship between photography and science. They use various methods and instruments to explain how long exposure photography can help measure the speed of an airplane, observe the rotation of the earth, or create light paintings.

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