Optical transfer functions for confocal theta fluorescence microscopy

Optical transfer functions are presented for the confocal theta fluorescence microscope, which uses an orthogonally placed objective lens to detect the fluorescence emission. Therefore the transfer functions do not exhibit cylindrical symmetry about the illumination axis. We show that in an ideal noise-free system, confocal theta microscopy increases the cutoff spatial frequency along the illumination axis by a factor of 3.5 to 3.7 for a numerical aperture of 0.75. In a system with 10% noise the improvement by confocal theta microscopy is even greater, between a factor of 4.1 and 4.4. This explains the improved three-dimensional imaging properties of theta microscopy.