| 摘要 |
Compact, low-cost keplerian variable-magnification viewfinders are disclosed that have a zoom ratio of at least 2 and simple composition that favorably corrects all aberrations. The viewfinders are useful for use with various types of cameras, and comprise a positive objective lens system and a positive ocular lens system. The objective lens system comprises, from the object side, first, second, and third lens groups preferably comprising a single negative lens, a single positive lens, and a single negative lens, respectively. Two of the first, second, and third lens groups are axially movable for adjusting the magnification of the viewfinder. The objective lens system preferably includes a fourth lens group preferably comprising a single positive lens. The ocular lens system preferably comprises at least a positive lens and a reflector array for producing an erect image. Several groups of embodiments satisfy respective conditional expressions.
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