| 摘要 |
A focus error detecting optical system has an optical parameter which makes a focus lock-in range by a focus error signal be a value capable of detecting focus on a front surface of a cover glass and focus on a back surface thereof separately. A control section, based on the focus error signal obtained by the focus error detecting optical system, brings a focal point of an observational optical system to a focus position. Further, focus error detecting optical systems include optical units each having an optical parameter corresponding to a numerical aperture of respective objective lenses. A control section selects the optical unit of the focus error detecting optical system corresponding to the objective lens in use. The control section, using a focus error signal obtained by the selected focus error detecting optical system, brings a focal point of an observational optical system to a focus position.
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