Optical sectioning
= Optical sectioning
<Optical sectioning> selects signal from a thin depth range of a specimen without physically cutting it. Repeating the measurement at successive focal depths gives a stack of sections from which three-dimensional organization can be reconstructed.
In a scanning <confocal microscope>, illumination is focused into the specimen and a detection pinhole rejects much of the <fluorescence> originating away from focus. A thick fluorescent specimen imaged with a wide-open and then a reduced pinhole demonstrates the rejected background; reducing the pinhole also discards useful <photons>, so section thickness and <signal-to-noise ratio> must be considered together.<Introductory Confocal Concepts by Nikon Instruments Inc.>[Opening discussion and Figures 1–2: rejection of out-of-focus signal and serial optical sections]{ref}