A triangular path shearing interferometer is described which can be used for the examination of large transparent objects. It has the advantage that it can be conveniently adapted to an existing schileren system, affording the possibility of quantitative measurements. The additional optical elements required are only of comparatively small aperture and are therefore quite inexpensive.
P. HARIHARAN and D. SEN, "Triangular Path Macro-Interferometer," J. Opt. Soc. Am. 49, 1105-1105 (1959)