Stereomicroscopes allow us to observe specimen structure three-dimensionally and perceive their depth. In general, three-dimensional images are derived from the brain’s interpretation of the two slightly different images received from each of the retinas. Stereomicroscopes utilize the functions of both eyes and brain to perceive depth by transmitting two images tilted at a small angle to generate stereoscopic vision. These microscopes are necessary for specimen micromanipulation or examination required in a large and comfortable working space. Some other features such as the wide field of view and variable magnification are also helpful for industrial micro-assembly, or for biological research that needs careful manipulation and vulnerable living organisms. However, a demand for wider variable magnification range has been increasing along with the various applications. We reported the “Perfect Zoom System” which can make some of the zoom lens groups move perpendicular to the optical axes in the low-power state as a solution to this problem in 2015. This technique improves the zoom ratio and enables more applications with additional parts. Here, we review developments in stereomicroscopes with the “Perfect Zoom System” and discuss its practical applications.
We can move an entrance pupil of a zoom lens from on-axis to off-axis by decentering lens groups of a zoom lens. This decentering zoom lens makes an objective lens of a stereomicroscope small. As a result, we can develop a stereomicroscope with high magnification and high resolution.
A stereomicroscope can stereoscopically observe an object with protrusions and recesses as if the object were viewed by both eyes. Such stereomicroscopes use an optical system to create two slightly different viewing angles of an object. The different images are both enlarged and viewed through two eyepieces. Each of the observation optical systems includes a variable magnification mechanism which is called a zoom lens system. In recent years, a demand for stereomicroscopes that can observe a wide variable magnification range has been increasing along with the diversification of applications. However, there are no stereomicroscope zoom lenses with both a high resolution and a large zoom ratio. We developed the “Perfect Zoom System” which can reduce the light flux diameter going through the objective lens in the low-power state. In the “Perfect Zoom System”, the zoom lens groups move along not only the optical axes but also perpendicular to the axes. Therefore, the objective lens could be made smaller by decentering the G2 and G3 group lenses in zoom lens group. We achieved a high resolution and a zoom ratio of 25:1.
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