Liquid-crystal image director for single-lens-reflex camera

摘要

The mirror in a single-lens-reflex (SLR) camera is eliminated by employing a liquid crystal cell and a polarizing beam splitter. The light from an illuminating lamp (32) is linearly polarized in a horizontal direction by a polarizer (58). The polarized illuminating light is totally reflected by a polarizing beam splitter (PBS) (54) and passes through a quarterwave plate (QWP) (56) and an objective lens (36). After passing through QWP (56) for the second time, the light is vertically polarized and totally passes through PBS (54). A focusing lens (40) focuses the image onto a film (30). A voltage supply (46) is connected to a liquid-crystal (LC) cell (44) by an electric switch (52) that can turn LC cell (44) on or off. When LC cell (44) is off, the polarization of the light is rotated by 90 DEG to be horizontally polarized. Thus the light is reflected by another PBS (48) to a prism (24) for viewing by a user (26). When the LC cell (44) is on, the light polarization is not rotated, and the light is transmitted through the PBS (48) to a mechanical shutter (28). During the shutter's (28) open period, an intense light pulse from a strobe lamp (42) illuminates a patient's eye (38) and exposes film (30). Shutter (28) can be eliminated since the LC cell (44) and the PBS (48) may also function as shutter.