Of particular interest were his publications in the area of wave optics, which addressed diffraction problems in the focal regions of
aplanatic systems. Using analytical tools, Kant was the first to solve problems of vector diffraction in
aplanatic systems with Seidel aberrations.
Eventually he obtained a general solution for aplanatic systems. His main published articles in those years were "The Minimum and Maximum Magnification of a Telescope" (1925) and "A Single-Lens Ocular Without Chromatic Difference of Magnification" (1929).
In his 1932 book, Aberration-free Reflecting Surfaces and Systems and New Methods for Testing Them, he discussed the pros and cons of aplanatic systems. He also described for the first time a null test for large telescope mirrors using an auxiliary spherical mirror of significantly smaller size.