The Pinhole Camera - Yousef's Notes

Simplest camera (basically just a small hole in a wall).

Pinhole cameras perform perspective projection.

Each point in the scene gets mapped to one single point in the image.

The size of the object in the image plane depends on the focal length and the distance of the object to the pinhole.

Using similar triangles, and with the image plane located at

A 3D straight line is also a straight line in the 2D image plane because the intersection of two planes (image plane and the plane formed by the straight line and the pinhole) is a straight line.

#Pinhole Size

In theory, the pinhole size sould be as small as possible because we want each point in the object be uniquely mapped to a single point in the image. If the pinhole is too large, several rays of light for a point get through and the image gets blurry.

However, if the hole is too small, it will result in diffraction where the image also gets blurry.

The ideal pinhole diameter is:

This expression leverages the geometric blur caused by large diameters (proportional to d) with the blur caused by diffraction (proportional to $f\lambda/d$). $\lambda$ for visible light is roughly 550nm.