We investigate three-dimensional transfer functions in order to understand image formation in the recently proposed 4Pi confocal microscope [
J. Opt. Soc. Am. A 9,
Opt. Commun. 93,
1992)]. Both nonfluorescence and fluorescence imaging methods are considered, and the effects of apodization functions are taken into account. It is shown that for a 4Pi confocal system of finite-sized aperture the cutoff spatial frequency in the axial direction is larger than that in the transverse direction; this behavior is opposite that of conventional confocal systems, explaining the observation of high axial resolution in 4Pi confocal systems. In addition, the three-dimensional optical transfer function for a conventional confocal fluorescence microscope of high aperture is presented.
© 1994 Optical Society of America
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