Shapiro and Shapiro
Dual focus optical system
 A dual focus optical system for causing the images of two objects separate from each other on the optical axis to be formed on the same image plane comprises a diverging element for causing a second light ray to diverge relative to a first light ray, a converging element provided on the object side of the diverging element for converging the second light ray relative to the first light ray, and an objective lens provided on the object side of the two elements for converging both of the first light ray and the second light ray. The objective lens is disposed so that the point of intersection between the first light ray and the second light ray in the composite system comprising the diverging element and the converging element is coincident with the focal plane of the objective lens which is adjacent to the converging element. 
Nippon Kogaku K.K.
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G03F G02B G02B G02B
inventional inventional inventional inventional
Kinya
Kato