Physics

The lens equation $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$ relates object distance $u$ and image distance $v$ for a fixed focal length. When you rearrange this to express $v$ as a function of $u$, you get a relationship where the product $(u - f)(v - f)$ is constant—this is the defining property of a rectangular hyperbola. The graph won't be a straight line because the relationship is nonlinear, and the asymptotes occur at the focal length.

The lens equation $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$ relates object distance $u$ and image distance $v$ for a fixed focal length. When you rearrange this to express $v$ as a function of $u$, you get a relationship where the product $(u - f)(v - f)$ is constant—this is the defining property of a rectangular hyperbola. The graph won't be a straight line because the relationship is nonlinear, and the asymptotes occur at the focal length.