Focussing condition detector

Claim 2

A focussing condition detector comprising a focussing lens which is movable along an optical axis; a photoelectric transducer element disposed at or adjacent to an imaging position of the focussing lens for detecting a focussing condition; processing means for performing an arithmetic operation on an output from the transducer element to derive an evaluation value according to a given formula, the processing means providing a decision output indicative of an in-focus or an out-of-focus condition of the focussing lens by comparing the evaluation value against a decision level, a decision level used when an image formed on the transducer element moves from a region representing an in-focus condition to another region representing an out-of-focus condition being different from a decision level which is used when the image moves in the opposite direction, adjacent to a threshold value representing a boundary between the in-focus and the out-of-focus region; and display means responsive to a decision output from the processing means to display a particular region which represents the focussing condition of the image.

Claim 3

A focussing condition detector according to claim 1 in which the transducer element comprises a plurality of aligned charge coupled devices which define light receivers of a reduced area.

Claim 4

A focussing condition detector according to claim 1 in which a pair of decision levels are defined on opposite sides of a threshold value representing a boundary between an in-focus region and an out-of-focus region representing a front pin and spaced therefrom by a given offset value, and another pair of decision levels are defined on the opposite sides of another threshold value representing a boundary between the in-focus region and another out-of-focus region representing the rear focus and spaced therefrom by an offset value.

Claim 5

A focussing condition detector according to claim 3 in which the offset value is chosen depending on a blurring between the optics and an object being photographed, electrical noise, the stroke of movement of the focussing lens and a change occurring in the evaluation value.

Claim 6

A focussing condition detector according to claim 1 in which the decision output may assume a variable value of -1, 0 and 1 which represent the front focus region, the in-focus region and the rear focus region, respectively.

Claim 7

A focussing condition detector according to claim 1 in which the display means comprises display elements connected to three output terminals of a display driver circuit for displaying the front focus, the rear focus and the in-focus condition, respectively, in response to the decision output.

Claim 8

A focussing condition detector according to claim 1 in which an output from the transducer element, the arithmetic operation to derive the evaluation value and the display occur at such a timing that the display means displays the result of the arithmetic operation from (n-1)-th cycle during the time the integrating operation for n-th cycle and the arthimetic operation therefor occur.

Claim 9

A focussing condition detector according to claim 1 in which the decision output is also fed to a motor drive circuit which is effective to drive the focussing lens into the in-focus condition.

Claim 10

A focussing condition detector according to claim 5 or 8 in which the motor drive circuit causes a motor to be driven in a forward or reverse direction or to be stopped when the decision output assumes a value of -1, 1 or 0, respectively.

Claim 11

In a camera having a movable taking lens, a drive means for selectively moving said taking lens, in a forward and rearward direction, a photoelectric transducer device for detecting light passing through said taking lens to develop a focussing condition signal S FC , representing the focussing condition of the image of the object being photographed, processing means for developing an evaluation value from said focussing condition signal (S FC ) for controlling the drive means to move the taking lens to bring the image of the object being photographed into focus in accordance with a method comprising the steps of: providing first and second boundary values (-X) and (+X), which define the boundary of an in-focus region bound on either side by out-of-focus regions respectively to the far and near side of the image of the object being photographed; providing first and second narrow offset regions extending on either side of each boundary value, the offset region embracing boundary value (-X) being defined by offset boundry values (-r-X) and (+r-X), and the offset region embracing boundary value (+X) being defined by offset boundary values (-r+X) and (+r+X), where +X<+r and (+r-X)<(-r+X); sampling the signal S FC at periodic intervals to determine its value; comparing the sampled value of the signal S FC with the offset boundary values in a predetermined sequence; operating said drive means to move the taking lens into the in-focus region whenever the sampled value of S FC is less than (-r-X) or is greater than (+r+X); halting said drive means whenever the sampled value of S FC is greater than (-X+r) and less than (+X-r); and moving said drive means in a direction determined by the previous sampled value of S FC whenever the presently sampled value of S FC lies in one of said offset regions.

Claim 12

In a camera having a movable taking lens, a drive means for selectively moving said taking lens, in a forward and rearward direction, a photoelectric transducer device for detecting light passing through said taking lens to develop a focussing condition signal S FC , representing the focussing condition of the image of the object being photographed, processing means for developing an evaluation value from said focussing condition signal (S FC ) for controlling the drive means to move the taking lens to bring the image of the object being photographed into focus in accordance with a method comprising the steps of: providing first and second boundary values (-X) and (+X), which define the boundary of an in-focus region bound on either side by out-of-focus regions respectively to the far and near side of the image of the object being photographed; providing first and second narrow offset regions extending on either side of each boundary value, the offset region embracing boundary value (-X) being defined by offset boundry values (-r-X) and (+r-X), and the offset region embracing boundary value (+X) being defined by offset boundary values (-r+X) and (+r+X), where +X<+r and (+r-X)<(-r+X); sampling the signal S FC at periodic intervals to determine its value; comparing the sampled value of the signal S FC with the offset boundary values in a predetermined sequence; operating said drive means to move the taking lens into the in-focus region whenever the sampled value of S FC is less than (-r-X) or is greater than (+r+X); halting said drive means whenever the sampled value of S FC is greater than (-X+r) and less than (+X-r); and moving said drive means in a direction determined by the previous sampled value of S FC whenever the presently sampled value of S FC lies in one of said offset regions.