Single-lens theta microscopy: Resolution, efficiency and working distance

In single-lens theta microscopy (SLTM), a single objective lens in combination with a mirror unit is used to achieve a theta configuration, which leads to axial and volume resolution improvements. In this type of microscope, the usable numerical aperture (NA) is not limited by the physical size of the objective lenses, as it is in two-lens theta microscopy. Although the outer parts of larger apertures are not entirely used, an increase in volume resolution by a factor of 2.9 can be achieved by increasing the NA from 0.75 to 1.1 in an orthogonal system. In addition, the angle between the faces of the mirror unit can be decreased in order to accommodate even larger NA and thereby to improve the spatial resolution further. The trade-off between resolution and collection efficiency improvements and the usable working distance in SLTM is also quantitatively discussed.