Practice question

Confocal microscopy improves contrast by placing a small pinhole aperture conjugate to focal plane before detector. This pinhole physically blocks photons originating above or below focus, transmitting only in-focus emission from specimen plane. By scanning point-by-point, sharp optical sections are collected without blur from out-of-focus light. Stacking sections enables 3D reconstruction of thick specimens. Objective lens and phase plates manage illumination, but pinhole is defining element for confocality, distinguishing it from widefield fluorescence where entire depth is illuminated simultaneously, reducing resolution and contrast.