Each plane within a set of conjugate planes is said to be conjugate with the others in that set because they are simultaneously in focus and can be viewed superimposed upon one another when observing specimens through the microscope. This interactive tutorial explores image-forming conjugate planes in the optical microscope.

	Interactive Java Tutorial
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The specimens utilized in this tutorial represent a variety of multiply stained plant thin sections captured with brightfield illumination. The tutorial initializes with a randomly selected specimen appearing out of focus in the microscope port window. To select a new specimen, use the Choose A Specimen pull-down menu. A set of sliders controls the focus of three conjugate planes in the microscope. The Sample Fine Focus slider can be used to focus the specimen, the equivalent of moving the stage or nosepiece up or down along the microscope optical axis. Adjustment of the field diaphragm focus is controlled by the Condenser Height slider, and the diaphragm aperture opening size and be changed with the Diaphragm Opening Size slider. The crosshair reticule positioned at the aperture diaphragm of the eyepiece can be brought into and out of focus with the Reticule Focus slider. In normal observation mode (using the eyepieces), the conjugate set of object or field planes can all be simultaneously viewed when the specimen is in focus. This observation mode is referred to as the orthoscopic mode, and the image is known as the orthoscopic image. Four conjugate planes can be brought simultaneously into focus using the sliders in this tutorial: the field diaphragm, the specimen plane, the intermediate image plane (reticule), and the observer's retina.