Camera Optics — The Physics in Your Lens
A camera is a light-tight box with a precision lens system that paints an image onto a sensor. Every setting you have ever touched — zoom, focus, aperture — is geometric optics in action.
Image formation by lenses
A converging lens refracts rays from each point of the scene so they meet again on the sensor, forming a real, inverted image. The lens equation 1/f = 1/do + 1/di tells the designer exactly where the sensor must sit for a given focus distance.
Aperture and depth of field
The aperture is an adjustable hole controlling light intake. A wide aperture (small f-number) gathers more light but accepts rays at steeper angles, shrinking the depth of field — the portrait-mode blur. A narrow aperture sharpens everything but needs longer exposure.
Focal length and zoom
Focal length sets magnification: longer focal lengths project a larger image of distant objects. Zoom lenses physically move element groups to change the effective focal length — pure applied lensmaker's optics.
Sensors and the photoelectric effect
Each pixel is a tiny photodiode: incoming photons knock electrons free (the photoelectric effect), and the collected charge becomes the brightness value. Bigger pixels collect more photons, which is why large sensors outperform small ones in the dark.
Try this yourself
- Cover a phone lens halfway with tape and take a photo — the image dims but stays complete, because every lens point sees the whole scene.
- Photograph a ruler at an angle with wide and narrow aperture (portrait vs landscape mode) to see depth of field change.
- Shine a laser pointer through a magnifying glass onto a wall to find its focal point.