A device as described for indicating the state of focus of an image of a document which is converted into a video signal by sequentially inspecting the incident light level at points within the image and generating an electrical signal having a parameter which varies with the light level. The device includes: (a) circuit responsive to the electrical signal from sequential inspection of the image for integrating the amplitude variations thereof to produce a varying amplitude focus indication signal, (b) amplifying means for generating from the varying amplitude signal a varying control signal, (c) an indicator comprising a linear array of lamps, (d) circuit which provides operating current for the lamps the current being related to the amplitude of the focus indication signal, so that with increasing amplitude of the latter more of the lamps are caused to be illuminated or vice versa, where all the lamps are illuminated to indicate a state of poor focus, and (e) means for ajusting the focus of the image in response to visual inspection of the illuminated lamps, so as to obtain the best possible indication of the state of focus of the image.

A lens focus control apparatus and method for use in a camera optical system and which is manually manipulated by a user, includes a lens position detector for detecting current positions of a focus lens and a zoom lens, a memory for storing a movable region value of the focus lens, a current position value of the focus lens and a contrast ratio value therein, and a display. The display indicates the current position of the focus lens, the range of movement of the focus lens, and the movement direction in the movable region of the focus lens. A microcomputer controls the above elements to adjust an exact focus and to display an exact focus direction using the contrast ratio value.

A focus detecting system has a signal processing circuit for processing output signals from photoelectric transducer elements and generating an output representing the focusing state. A circuit is provided to stabilize the output against abrupt changes in focusing condition.

There is provided an automatic focus control device for use in a camera system comprising a focus detection control means for continuously driving a motor from the time when it is judged that a focus condition of a photograph lens can not be detected until it is judged that the focus condition can be detected, and a rotation number control means for controlling the rotation speed of said motor driven by said focus detection control means in accordance with a constant data designating a relationship between the rotation number of said motor and a unit of a defocus value. Accordingly, the moving speed of said photograph lens is controlled in accordance with defocus variation during the movement of said photograph lens, resulting in that the infocus position of the object can be detected by a low contrast search without overrunning the infocus position, even though the object is positioned far from an available range of the focus detection.

Apparatus for use with a focus detecting device arranged to repeatedly detect a state of focus, or for use with a camera having such a focus detecting device includes a processor for determining whether the state of focus detected by the focus detecting device is an in-focus state or an out-of-focus state. An indicator provides an indication of the in-focus state in response to the processor determining that the in-focus state has been detected. The processor causes the indication provided by the indicator to vary on the basis of a number of times that the in-focus state has been determined by the processor.