| 摘要 |
An eyepiece optical system, which is used in a single lens reflex camera having a penta mirror, includes a negative first single lens element, a positive second single lens element, and a negative third single lens element, in this order from the penta mirror; wherein the second single lens element is a diopter adjusting lens element which is adjustable along the optical axis; and the following conditions are satisfied:whereinf1 designates the focal length of the first single lens elements;f2 designates the focal length of the second single lens element;f3 designates the focal length of the third single lens element; andfe designates the focal length of the entire eyepiece optical system when the diopter is -1.0.
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