Bath Interferometer Astigmatism Calculator

DFTFringe has a handy calculator that can tell you how much your Bath beam separation creates astigmatism. This whole topic is kind of moot as if you use DFTFringe properly where you image the mirror in one position and then rotate the mirror 90 degrees and get more igrams in this second rotation, then you can eliminate many sources of astigmatism.
Still it's an interesting topic and highlights simulated igrams feature in DFTFringe.