The Multiple-Sine-Slit Microdensitometer (MSSM) measures transmittance modulation by scanning the sample with a sinusoidal irradiance distribution generated by laser two-beam interference. The theory of the instrument is derived both from conventional microdensitometry and from treating the sample as a complex valued grating that diffracts two impinging coherent fields. The instrument has a constant MTF of 0.5; its principle disregards any phase modulations in the sample; and its large measuring area improves signal-to-noise ratio by 1-2 orders of magnitude. These are necessary qualifications for determining the MTF of recording materials of very high resolution. With a He-Ne laser, the range of the MSSM spans from 4 c/mm to 1500 c/mm. The practical implementations of the evaluation of film MTF's with this system are described.
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Johansson et al. (1974) studied this question.
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