Things To Try

Turn on the flashlight and hold the magnifying glass in front of it to project the image onto a wall. Try adjusting the distance between the magnifying glass and the flashlight to focus your image.

How It Works

When a picture is taken with a camera, the lens gathers and focuses light to produce a small upside-down image on the image sensor (see Figure 1).  Now imagine if the sensor were replaced by a small light source, like a flashlight.  The light rays would then move in exactly the opposite direction. The same lens would produce a large image outside the camera that could be focused on a screen.  The camera is now a projector (see Figure 2).

Figure 1: Image formation in a camera

Figure 2: Image formation with a projector

In the slide projector that you built, the light from the flashlight passes through the transcluscent slide.  The hand-held lens then focuses the light onto a screen.  In an actual slide projector the slides and the lens would be housed inside a single box.

Bigshot Connections

• Learn: Imaging Lens
• Fun: Buildables: Make a Simple Camera Model

Fun Facts

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References