What is the term for the phenomenon where light reflected from a single point in space causes an out-of-focus image?

The phenomenon where light reflected from a single point in space causes an out-of-focus image is known as Circles of Confusion. This term refers to the blurry spots created when light rays from a point source do not converge at a single point on the image sensor, resulting in a point being rendered as a small circle in the image rather than a sharp dot.

This occurs when the lens is not perfectly focused on the subject; objects at varying distances from the focal point will exhibit different sizes of circles of confusion, with further distances leading to larger circles, contributing to an overall perception of softness or blurriness in the image. Understanding circles of confusion is crucial for photographers to achieve desired depth of field and focus characteristics in their images, as it helps in visualizing how different elements in the frame will appear in terms of sharpness and clarity.

The other terms, while related to optics and photography, refer to different concepts. Diffraction relates to the spreading of light waves as they pass through a small aperture, Depth of Field pertains to the range of distance within a photo that appears acceptably sharp, and Field Curvature describes how a flat subject is rendered on a curved plane, impacting focus across the frame. Each of these concepts plays a role