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

• 
• 
• 

"It Must be magic!"

In the 1600's, the earliest slide projectors were named "magic lanterns."  Their viewers couldn't understand where such large, colorful images could have come from.  Their only explanation for this amazing experience was magic [1].

Pocket Projectors

With the miniaturization of light and power sources, projectors have shrunken in size over the past decade.  Today, some projectors are even small enough to fit inone's pockets or be part of mobile phones.

Stitching Images on the Wall

When we try to project images on very a large screen, such as a planetarium dome, regular projectors sometimes do not have enough resolution to produce a sharp image.  Multiple projectors may be used in these cases.  The image to be projected is divided up among the projectors, which are carefully aligned to produce a single large image.

References