Optics & Image Formation: Physical Mechanisms

Key elements include the objective or primary mirror, focal plane, secondary optics, eyepiece or detector, and baffling. Image scale depends on focal length and detector geometry, while field of view depends on both optics and sensor size.

A curved optical surface changes the direction of incoming rays so rays from a given sky direction converge near a corresponding point in the focal plane. Aberrations occur when real optics depart from the ideal mapping.

Ray tracing predicts image positions and aberrations, while laboratory star tests and measured point-spread functions show how an actual optical system performs across the field.

Refraction follows the change in wave speed across media and Snell's law, while reflection follows equal incidence and reflection angles for ideal surfaces. Curved optical surfaces are shaped so rays from a common direction converge. Diffraction prevents any finite aperture from producing a perfect point image, so geometric ray tracing eventually gives way to wave optics. Focus errors broaden the point-spread function even when all other optics are ideal.