When the recognition of the arrangement in space of small objects is desired a stereoscopic lens can be used.
On the other hand, a very much exaggerated stereoscopic effect can be derived from short focused ?
If the perspective centres lie too near one another in the object-space, as may happen with slightly opened and weak systems, the difference of the perspective is then too slight to make any real stereoscopic impression.
On account of the slight depth definition, short focused systems of wide aperture are not at all specially suitable for stereoscopic observation, because the possibility of observing objects taking up a good deal of space is too limited when such systems are used.
A second manner of making stereoscopic observations employs stereoscopic eyepieces.