초록 ▼

The disclosure is directed to a focus detection device which is provided with first to third reference signal generators for generating reference signals which are compared with a focus condition signal varying with the amount and direction of the adjustment required for the objective lens to focus

The disclosure is directed to a focus detection device which is provided with first to third reference signal generators for generating reference signals which are compared with a focus condition signal varying with the amount and direction of the adjustment required for the objective lens to focus on a target object, and also, to an automatic focusing device for a camera, which is equipped with an objective lens operating system for the focusing, and a motor for controlling the objective lens operating system in response to a signal from a focus condition determining means.

대표청구항 ▼

1. A focus detection device comprising: an objective lens adjustable for focusing; a focus condition signal generating means for generating a focus condition signal which varies with the amount and direction of the adjustment required for said objective lens to focus on a target object; a refer

1. A focus detection device comprising: an objective lens adjustable for focusing; a focus condition signal generating means for generating a focus condition signal which varies with the amount and direction of the adjustment required for said objective lens to focus on a target object; a reference signal generating means for generating first to third reference signals, said first and second reference signals being larger and smaller than said third reference signal by a predetermined value, respectively; a focus condition determining means switchable between a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said first and second reference signals, said focus condition determining means being adapted to determine that said objective lens is in an in-focus condition with respect to the target object, with said focus condition signal reaching said third reference signal in said first operation mode, and with said focus condition signal remaining within the range between said first and second reference signals in said second operation mode, respectively; and a switching means for switching said focus condition determining means from said first operation mode to said second operation mode when said focus condition determining means in said first operation mode has determined that said objective lens is in an in-focus condition with respect to the target object. 2. A focus detection device as defined in claim 1 wherein said focus condition determining means includes a first comparator having first and second input terminals connected to receive said focus condition signal and said first and third reference signals respectively and a second comparator having first and second input terminals connected to receive said focus condition signal and said second and third reference signals. 3. A focus condition detection device as defined in claim 2, wherein said switching means includes a first switching element for causing said first and third reference signals to be selectively input to said second input terminal of said first comparator and a second switching element for causing said second and third reference signals to be selectively input to said second input terminal of said second comparator, said first switching element being responsive to an output of said first comparator generated with said focus condition signal reaching said third reference signal for causing said first reference signal to be input to said second input terminal of said first comparator, while said second switching element is responsive to an output of said second comparator generated with said focus condition signal reaching said third reference signal for causing said second reference signal to be input to said second input terminal of said second comparator. 4. A focus condition detection device as defined in claim 3 wherein said focus condition signal generating means is adapted to generate said focus condition signal as an analogue voltage signal, said reference signal generating means is adapted to generate said first to third reference signals as analogue voltage signals, and said first and second comparators are analogue voltage comparators. 5. A focus detection device as defined in claim 4 wherein said reference signal generating means includes first and second impedance elements for providing the predetermined level difference between said first and third reference signals and between said second and third reference signals, respectively. 6. A focus detection device as defined in claim 5 wherein said first switching element is arranged to selectively make said first impedance element effective and in-effective, and said second switching element is arranged to selectively make said second impedance element effective and in-effective. 7. A focus detection device as defined in claim 6 wherein said first and second impedance elements are resistors. 8. A focus detection device as defined in claim 1 wherein said focus condition signal generating means includes a light emitting element for emitting a light towards the target object, first and second photosensitive means supported at a position spaced from said light emitting element by a given distance to be angularly displaceable and to receive said light reflected at the target object respectively for generating outputs which vary with the distance between the target object and said device and the angular position of said photosensitive means, a control means for angularly displacing said first and second photosensitive means in accordance with the adjusted position of said objective lens and for means processing said outputs of said first and second photosensitive means to produce said focus condition signal. 9. An automatic-focusing device for a camera comprising: an objective lens adjustable for focusing; a focus condition signal generating means for generating a focus condition signal which varies with the amount and direction of the adjustment required for said objective lens to focus on an object to be photographed; a reference signal generating means for generating first to third reference signals, said first reference signal and said second reference signal being larger and smaller than said third reference signal by a predetermined value, respectively; a focus condition determining means switchable between a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said first and second reference signals, said focus condition determining means in said first operation mode generating an in-focus signal representing that said objective lens is in an in-focus condition with respect to the object to be photographed, with said focus condition signal reaching said third reference signal and an out-of-focus signal representing that said objective lens is in an out-of-focus condition without said focus condition signal reaching said third reference signal, whereas said focus condition determining means in said second operation mode continues to generate said in-focus condition signal unless said focus condition signal goes out of the range between said first and second reference signals; an objective lens drive means for driving said objective lens for the adjustment thereof; a drive control means for causing said objective lens drive means to drive said objective lens in response to said out-of-focus signal and to stop the driving in response to said in-focus signal; and a switching means for switching said focus condition determining means from said first operation mode to said second operation mode in response to said in-focus signal. 10. An automatic-focusing device for a camera as defined in claim 9, wherein said focus condition signal is larger than said first reference signal when the adjustment in one direction is required for said objective lens to focus on the object to be photographed and said focus condition signal is smaller than said second reference signal when the adjustment in an opposite direction is required for said objective lens to focus on the object to be photographed. 11. An automatic-focusing device for a camera as defined in claim 10, wherein said out-of-focus signal represents the direction of adjustment required for said objective lens to focus on the object to be photographed, depending on whether said focus condition signal is larger than said third reference signal when said focus condition determining means is in said first operation mode and depending on whether said focus condition signal is larger than said first reference signal or smaller than said second reference signal when said focus condition determining means is in said second operation mode respectively. 12. An automatic-focusing device for a camera as defined in claim 11 wherein said focus condition determining means includes a first comparator having first and second input terminals connected to receive said focus condition signal and said first and third reference signals respectively and a second comparator having first and second input terminals connected to receive said focus condition signal and said second and third reference signals. 13. An automatic-focusing device for a camera as defined in claim 12, wherein said switching means includes a first switching element for causing said first and third reference signals to be selectively input to said second input terminal of said first comparator and a second switching element for causing said second and third reference signals to be selectively input to said second input terminal of said second comparator, said first switching element being responsive to an output of said first comparator generated with said focus condition signal reaching said third reference signal for causing said first reference signal to be input to said second input terminal of said first comparator, while said second switching element is responsive to an output of said second comparator generated with said focus condition signal reaching said third reference signal for causing said second reference signal to be input to said second input terminal of said second comparator. 14. An automatic-focusing device for a camera as defined in claim 13 wherein said focus condition signal generating means is adapted to generate said focus condition signal as an analogue voltage signal, said reference signal generating means is adapted to generate said first to third reference signals as analogue voltage signals and said first and second comparators are analogue voltage comparators. 15. An automatic-focusing device for a camera as defined in claim 14 wherein said reference signal generating means includes first and second impedance elements for providing a predetermined level difference between said first and third reference signals and between said second and third reference signals, respectively. 16. An automatic-focusing device for a camera as defined in claim 15 wherein said first switching element is arranged to selectively make said first impedance element effective and in-effective and said second switching element is arranged to selectively make said second impedance element effective and in-effective. 17. An automatic-focusing device for a camera as defined in claim 16 wherein said first and second impedance elements are resistors. 18. An automatic-focusing device for a camera as defined in claim 9 wherein said focus condition signal generating means includes a light emitting element for emitting a light towards the obejct to be photographed, first and second photosensitive means supported at a position spaced from said light emitting element by a given distance to be angularly displaceable and to receive said light reflected at the object to be photographed respectively for generating outputs which vary with the distance between the object to be photographed and said device and the angular position of said photosensitive means, a control means for angularly displacing said first and second photosensitive means in accordance with the adjusted position of said objective lens and for means processing said outputs of said first and second photosensitive means to produce said focus condition signal. 19. A focus detection device comprising: an objective lens adjustable for focusing; a focus condition signal generating means for generating a focus condition signal which is in the form of an analogue voltage and which varies with the amount and direction of the adjustment required for said objective lens to focus on a target object; a reference signal generating means for generating first to third reference signals which are each respectively in the form of an analogue voltage, said first and second reference signals being larger and smaller than said third reference signal by a predtermined value, respectively; a first comparator selectively settable to one of a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said first reference signal and adapted to change its output depending on the comparison result in each of its first and second operation modes; a second comparator selectively settable to one of a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said second reference signal and adapted to change its output depending on the comparison result in each of its first and second operation modes, the combination of the outputs of said first and second comparators generated with at least one of said first and second comparators set to its first operation mode and with said focus condition signal reaching said third reference signal being an in-focus signal representing that said objective lens has been adjusted to an in-focus condition; and a setting means for setting said first and second comparators to their second operation mode upon generation of said in-focus signal so that the generation of said in-focus signal continues until said focus condition signal goes out of the range between said first and second reference signals, while originally setting at least one of said first and second comparators to its first operation mode. 20. A focus condition detection device as defined in claim 19, wherein said setting means includes: a first setting member for selectively setting said first comparator to one of its first and second operation modes, said first setting member setting said first comparator to its first operation mode when said focus condition signal is originally larger than said first reference signal while setting the same to its second operation mode when said focus condition signal decreases and reaches said third reference signal to change the output of said first comparator; and a second setting member for selectively setting said second comparator to one of its first and second operation modes, said second setting member setting said second comparator to its first operation mode when said focus condition signal is originally smaller than said second reference signal while setting the same to its second operation mode when said focus condition signal increases and reaches said third reference signal to change the output of said second comparator. 21. A focus condition detection device as defined in claim 20, wherein said first comparator includes a first input terminal connected to receive said focus condition signal and a second input terminal connected to receive said first and third reference signals, said second comparator includes a first input terminal connected to receive said focus condition signal and a second input terminal connected to receive said second and third reference signals, said first setting member includes a first switching element for causing said first reference signal, in place of said third reference signal, to be input to said second input terminal of said first comparator in response to the change of the output of said first comparator due to said focus condition signal reaching said third referene signal, and said second setting member includes a second switching element for causing said second reference signal, in place of said third reference signal, to be input to said second input terminal of said second comparator in response to the change of the output of said second comparator due to said focus condition signal reaching said third reference signal. 22. An automatic focusing device for a camera, comprising: an objective lens adjustable for focusing; an objective lens drive means for driving said objective lens for its adjustment for focusing; a focus condition signal generating means for generating a focus condition signal which is in the form of an analogue voltage and which varies with the amount and direction of the adjustment required for said objective lens to focus on an object to be photographed; a reference signal generating means for generating first to third reference signals which are each respectively in the form of an analogue voltage, said first and second reference signals being larger and smaller than said third reference signal by a predetermined value, respectively; a first comparator selectively settable to one of a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said first reference signal, and adapted to change its output depending on the comparison result in each of its first and second operation modes; a second comparator selectively settable to one of a first operation mode for comparing said focus condition signal with said third reference signal and a second operation mode for comparing said focus condition signal with said second reference signal and adapted to change its output depending on the comparison result in each of its first and second operation modes, the combination of the outputs of said first and second comparators generated with at least one of said first and second comparators set to its first operation mode and with said focus condition signal reaching said third reference signal being an in-focus signal representing that said objective lens has been adjusted to an in-focus condition; a setting means for setting said first and second comparators to their second operation mode upon generation of said in-focus signal so that the generation of said in-focus signal continues until said focus condition signal goes out of the range between said first and second reference signals, while originally setting at least one of said first and second comparator to its first operation mode; and a drive control means for causing said objective lens drive means to drive said objective lens in accordance with the outputs of said first and second comparators and to stop the driving in response to said in-focus signal.