| 摘要 |
Provided is an adapter optical system attachable between an image pickup lens and a camera body, the adapter optical system including, in order from an object side: a first optical unit having negative refractive power; a second optical unit that is insertable in and removable from an optical path; and a third optical unit having positive refractive power, in which the following expression is satisfied: 0.03<|αa2|<0.50, where αa2 represents an incident converted inclination angle obtained by normalizing an incident inclination angle of an axial beam entering the second optical unit inserted in an optical path with an exit inclination angle of an axial paraxial ray emerging from a surface closest to an image plane side in the adapter optical system being set to one (1).
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