Calcium-release waves of extremely short duration passing across a cell can now be tracked with these confocal instruments. They last 100 milliseconds or so. With a regular confocal microscope, it would be a matter of chance if you ever saw one of these things at all. And you certainly couldn't follow its course in the way that we can. To do this, a point of laser light under computer control is scanned across a specimen, usually fluorescently labeled, at a set depth.
Light returning from the specimen then passes through a pinhole aperture called a spatial filter.
The remaining sharply focused light strikes a photomultiplier tube, and, with computer assistance, is used to construct an image, called an optical slice. A large amount of the illuminating light is lost at the pinhole aperture in the confocal process, which is one reason laser light sources have proved so important. Because of the initial intensity of lasers, the in-focus light reaching the photomultiplier tube retains enough brightness to create full images. The confocal microscope can create these images even when the specimen is relatively thick or translucent, and optical slices from different depths can be used to build striking three- dimensional images of a cell. Coupled with the faster image- capture rates now possible, confocal images are opening up many new lines of cell dynamics investigations.