## Section48.5Pinhole Camera

A pinhole camera is an optical device that projects inverted image of an object on a screen without using any lens or mirror. It can be easily made from a cardboard box and a wax paper. Replace one side of the cardboard box by a wax paper to serve as the screen. Make a small hole in the middle of the opposite side.

Rays of light from an object pass the hole and meet on the screen and make an inverted image as shown in Figure 48.5.1.

A detector such as a photographic plate may be placed in place of the wax paper at the back side to record the image. Pin-hole camera is useful for viewing a solar eclipse where you can look at the image of the sun instead of looking at the sun directly.

### Subsection48.5.1F/# of a Pinhole Camera

Let $D$ be the diameter of the room and $L$ the distance from the hole to the back wall of the room where image is projected. This $L$ serves as the replacement of the focal length $f$ in case of a lens. Therefore, F/# of the pinhole can be written as

\begin{equation*} F/\# = \frac{L}{D}. \end{equation*}