Greenough, employs two systems for setting up the image, in order to avoid the pseudoscopic effect.
In the oldest microscope by Cherubin d'Orleans the observer receives a pseudoscopic impression in consequence of the reversed image.
Turning the diaphragms 180° round the optical axis, the orthoscopic impression can be changed into the pseudoscopic. The mechanical arrangement of the eyepiece is such that the distance of the two exit pupils can be adjusted to the interpupillary distance.
Depressions appeared as elevations, and vice versa, or, as we must say after Charles Wheatstone, it presented a pseudoscopic impression; this quality, however, was not recognized by the microscopists of the time.