| 摘要 |
PURPOSE:To enable focus detection at various positions in a visual field and to obtain high focus detection accuracy and image forming performance by composing a secondary image formation system of >=2 lenses with positive refracting power, and making at least one of their lens surfaces aspherical. CONSTITUTION:The secondary image formation optical system consists of a lens system which is arranged behind a brightness stop 25 and equipped with at least two lenses 26 and 27 having positive refracting power while at least one surface is made aspherical. A 2nd lens which causes trouble in correcting the aberration of both a pupil system and a visual field system excellently like a conventional example can, therefore, be omitted. Consequently, the aberrations of the pupil system can be compensated sufficiently by a condenser lens 24 and the aberration of the visual field system can be compensated sufficiently by the lens which has the positive refracting power and is arranged behind a brightness stop. Consequently, one optional couple of secondary images can be formed on a photoelectric converting element over the wide visual field range of a body without providing many secondary image formation optical systems successively, and the high focus detection accuracy and image formation performance can be obtained. |
