Beam Path in Confocal LSM
In the mid-1950s, Princeton University researcher Marvin Minsky sought a way to increase signal-to-noise when imaging central nervous system samples. Because CNS tissue is very dense and scatters light, fluorescently dyed brain cells looked blurry when viewed under a conventional widefield microscope. To counter this problem, Minsky placed a pinhole aperture at the emission side of the objective. Conjugated with the focal point of the lens (hence, "confocal"), the pinhole allowed in-focus light to reach the detector while blocking light emanating from regions above and below the focal plane (see box 1). In essence, it allowed him to view virtual "optical slices" through the haze of thick tissue.
But the resulting image, however sharp, represented just a small piece of a single optical slice. To image a complete slice, the entire plane had to be scanned. Today there are two primary...