The effects of aperture modulation are investigated in a Korean binocular objective lens in isolation from the rest of the system. The axial aberration characteristics are derived through computation from the design data. The MTF is measured for modulated apertures in the presence of axial aberration. The aperture modulation is carried out by providing a mask which has an opaque annulus on an optical flat and is in contact with the lens under test. The MTF varies with the area and the position of the opaque annulus. The MTF of the lens is improved by properly positioning the opaque annulus. The MTF curves with the modulated aperture are also compared with the constricted circular aperture having the same area as the modulated one. The performance of many optical systems can be improved by proper aperture modulation.
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