The magnification of a single prism or a series of prisms is normally considered in a situation when collimated light is incident, which is equivalent to placing the object at a very large distance from the prism system. This is the usual situation considered and described in most of the literature. In such cases, the magnification is referred to as the anamorphic magnification of the prism system in collimated light. However, when the object is at a finite distance, the apparent magnification is quite different and sometimes is just the reciprocal of what it would be if the object were at infinity. These situations are analyzed for the case of Brewster prisms, and the results can be checked visually very easily in ordinary white-light illumination because of the mutual cancellation of the dispersion of the Brewster prisms.
M. V. R. K. Murty,
Jesus R. Moya-Cessa,
"Magnification Of Prisms: An Apparent Anomaly And Its Explanation," Optical Engineering 23(1), 230183 (1 February 1984). https://doi.org/10.1117/12.7973258