A Camera with No Lens
The pinhole camera — straight lines make pictures
What this lesson covers
Why it matters
A shoebox, a pin-prick, and a piece of tracing paper — and suddenly there's a tiny MOVING picture of the world inside the box. Upside-down, mind you. Straight lines did that.
Predict first
The image in a pinhole camera is upside-down because…
Rays from the TOP of the candle pass straight through the hole to the BOTTOM of the screen, and vice versa — the crossing writes the picture upside-down.
- light rays travel straight and CROSS at the tiny hole — correct
- the box flips the picture
- it isn't — it's upright
What you do
Walk the candle nearer and farther — watch the upside-down picture grow and shrink, ruled entirely by straight lines.
Check yourself
The pinhole camera works WITHOUT a lens because…
One ray per point, straight through the hole — geometry is the only equipment.
Bring the candle CLOSER to the pinhole and its image gets…
Steeper rays through the hole spread wider on the screen — closer means bigger (still upside-down!).
Making the pinhole much BIGGER makes the image…
A big hole lets many overlapping straight-line pictures in at once — bright mush. Tiny hole, sharp picture.
- light's straight-line travel through a tiny hole makes the image by itself — correct
- there is a hidden lens
- the box is dark
- bigger — correct
- smaller
- the right way up
- brighter but blurry — correct
- sharper
- disappear