| 摘要 |
A viewing tube of a microscope is provided with a circumferential slot, and a slider carrying an optical element, such as a reticle, is removably received through the slot to position the optical element on an optical axis of the viewing tube proximate to an insertion end of an eyepiece received by the viewing tube. A collar or other cover means is provided to close off the slot when it is not in use. The invention enables quick change of optical elements in the viewing tube without removal of the eyepiece from the viewing tube.
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