PURPOSE: To prevent deterioration in focusing precision due to the eccentricity of a projection lens and to attain precise focusing detection by providing two photodetecting means symmetrically about a plane containing the optical axis of the projection lens.
CONSTITUTION: Two photodetecting means consisting of photodetection lenses 31 and 32 and photodetecting elements 41 and 42 are provided in parallel symmetrically about the optical axis O of the projection lens 1 and a light emitting element 2, and the distance R to a subject is determined from the mean value of image formation positions D1 and D2 of pieces of photodetection luminous flux of both photodetecting elements 41 and 42. When the lens 1 has eccentricity ΔY from the optical axis O of the projection lens 1, said image formation position D1 and D2 are eccentric as shown positions D1' and D2' to have errors ΔD1 and ΔD2 respectively. Those errors are equal in the opposite directions, so the mean value of the image formation positions D1' and D2' is equivalent to the mean value of the correct image formation position D1 and D2 and the correct subject distance is determined accurately, thereby adjusting the focus of the photographic lens accurately.
FUJIBAYASHI KAZUO
OOTAKA KEIJI
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