Ophthalmic instrument having a focus detecting system

Details Ophthalmic instrument having a focus detecting system Ophthalmic instrument having a focus detecting system

1984-03-29

1986-12-02

Bovernick, Rodney B.

Optics: eye examining, vision testing and correcting

Eye examining or testing instrument

Objective type

351206, A61B 314

Patent

active

046260897

ABSTRACT:
An eyefundus camera including an observing and photographing optical system having a focusing lens, a mark projecting optical system for projecting a plurality of mark images on patient's eyefundus. The mark projecting optical system is interconnected with the focusing lens of the observing and photographing optical system. There is provided a focusing signal detecting device including a photoelectric device for photoelectrically scanning the mark images projected on the fundus of the patient's eye to produce mark image signals, a horizontal synchronizing signal counting circuit for counting horizontal synchronizing signals for the photoelectric means, a mark image counting circuit for counting number of the mark image signals to determine that a predetermined number of mark image signals exist in a single scanning line, an operation circuit responsive to outputs of the two circuits for determining a horizontal scanning line which is used for judgement of focus conditions.

REFERENCES:
patent: 4436388 (1984-03-01), Takahashi et al.

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