| 摘要 |
The invention is directed to a diopter movement type of finder optical system for single-lens reflex cameras, which is well corrected in terms of various aberrations such as spherical aberration and off-axis aberrations, is of resolution so high that the image can be well viewed, and has a short overall length or is compact. This finder optical system comprises, in order from the side of the eye point EP, a first lens 2 having positive refracting power, a second lens 3 having positive refracting power, a third lens 4 having negative refracting power and a pentaprism 5, with the first and second lenses 2 and 3 being moved together in the optical axis direction for diopter movement while the third lens 4 remains fixed. Moreover, the finder optical system conforms to four conditions regarding the focal lengths of the first to third lenses and the composite focal length of the first and second lenses 2 and 3.
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