| 摘要 |
Temporal changes in an object are detected by focusing light from preselected spatial locations of the object on associated first and second regions of a light sensitive target at first and second times, respectively, and by comparing the light intensity focused on the regions. The focusing apparatus includes a Ronchi grating located at an image plane between the object and a light sensitive target. At the first time, light from the object passes through the clear portions of the grating to illuminate alternate parallel stripes on the target, while at the second time, the light passing through the clear portions is shifted to illuminate the regions between the first parallel stripes. The target is then scanned, and information from associated stripes is compared to detect changes. In one embodiment, the shaft can be brought about by the use of a birefringent crystal and polarized light; alternatively, a beam splitter and a shutter arrangement can be used.
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