= Stereomicroscope
A <stereomicroscope> is an <optical microscope> that sends distinct views of the same specimen to the two eyes through separate viewing channels. The views originate at slightly different directions, producing <stereo disparity> that supports <stereoscopy>. Two <microscope eyepieces> alone do not establish stereo imaging: splitting one image into identical copies supplies no second viewpoint.
A two-objective arrangement uses separate <microscope objective> assemblies whose viewing directions converge on the specimen. A shared-objective arrangement can instead preserve two distinct viewing bundles through one main objective. The distinction concerns how the two perspectives are formed, rather than the number of eyepieces. A primary manufacturer manual gives a concrete two-path example: its S-series optics have a10° convergence angle and a compact lower assembly providing access around the specimen.<Leica S Series User Manual by Leica Microsystems>[Printed p.13, “What Your Stereo Microscope has to Offer you”, optical paths and specimen access]{ref}
For an original geometric illustration, take two viewing rays inclined by $\pm\alpha$ to the normal of a reference plane. A feature at height $h$ above that plane has ray intersections displaced in opposite directions by $h\tan\alpha$, so their separation is
$$
d=2h\tan\alpha.
$$
With total convergence angle $2\alpha=10^\circ$ and $h=1\,\mathrm{mm}$, the separation is about0.175mm. This back-projected reference-plane geometry illustrates <stereoscopic triangulation>; it is not a specification of human depth accuracy or a universal pixel-to-height calibration. Actual image coordinates also depend on each channel's optics and alignment.
The distinct viewpoints are useful when positioning a fine tool near a surface, inspecting a small mechanical assembly or distinguishing raised features from flat markings. Illumination reflected from an opaque surface makes many such specimens accessible without preparing a thin transmitting section. The <microscope working distance> determines how much physical room remains between the instrument and the focused specimen, which matters when a probe or tool must enter that space.
For measurement, retain the magnification setting and calibrate the relevant channel with a <stage micrometer>. A scale calibration in a reference plane does not automatically convert stereo displacement into height; that requires the viewing geometry or a separate height calibration. Increasing magnification also does not guarantee improved <diffraction-limited resolution>. The purpose of the second view is geometric information, alongside the instrument's ability to resolve and magnify structure.
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