All of conventional methods to calculate wave-optical MTF values are based on a physical presumption that a point amplitude distribution formed by an optical system can be obtained as a result of Fourier transform of the pupil function which corresponds to an object point. Methods based on the above presumption are named here “Fourier transform methods”. There are some uncertainties about the accuracy of values obtained with these methods, especially when they are applied to optical systems which have extremely large aperture ratio or extremely wide angle of view. It can be shown that these uncertainties come from the above presumption. To find out the way of obtaining accurate values and also to find out some practical methods of increased accuracy, processes of calculation are reexamined, starting from the original Kirchhoff's diffraction integral. As a result of the investigation, three methods are proposed.
The most fundamental method is to numerically calculate Kirchhoff's diffraction integral itself (“method K”). On the other hand, it is shown that two steps of improvement can be expected even within the scope of “Fourier transform methods”. Thus two methods are developed (“method A” and “method B”).
To examine the feasibility of these three methods, several sample lenses are specially selected and their MTF values are calculated by use of these methods. The results are compared among one another and also with the values obtained by a typical conventional method.

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The formation of interference fringes in Leendertz's interferometer is discussed on the basis of a nonlinear recording effect of photographic plates.

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