Fixed vision system comprising: - a sensor, comprising an array of light sensitive elements, for acquiring an image of an object on a detecting plane, said sensor comprising a sensitive surface; - a light-emitting device for generating a luminous reference figure on said detecting plane, said light-emitting device comprising at least a first LED having a respective emission surface; - at least an objective having an optical axis through which a luminous radiation and a further luminous radiation pass, said luminous radiation coming from said object and being directed to said sensor and said further luminous radiation coming from said light-emitting device and being directed to said object, said luminous radiation defining between said detecting plane and said sensitive surface an optical path passing through said objective and said further luminous radiation defining between said detecting plane and said emission surface of said first LED a further optical path passing through said objective; - said sensor and said light-emitting device being positioned in such a way that, when said detecting plane is focused by said objective on said sensor, said sensitive surface of said sensor is on an image plane (60; 73) generated by said objective and said emission surface of said first LED is on a first plane which is a mirror plane with respect to said image plane (60; 73); said vision system further comprising: - deflecting means (25, 26) comprising a first mirror interposed between said first LED and said objective arranged for deviating said further luminous radiation from said emission surface of said first LED and generating said mirror plane, characterized in that said light-emitting device comprises a second LED having a respective emission surface, said deflecting means (25, 26) comprising a second mirror interposed between said second LED and said objective arranged for deviating a further respective luminous radiation coming from said emission surfaces of said second LED such that said emission surface of said second LED is positioned on a second plane which is a mirror plane with respect to said image plane (60; 73), between said detecting plane and said emission surface of said second LED being defined a still further optical path passing through said objective such that a focusing condition of said detecting plane on said sensor corresponds to a focusing condition of said luminous reference figure on said detecting plane so that the focusing of said vision system is checkable during installation with the naked eye. - a sensor, comprising an array of light sensitive elements, for acquiring an image of an object on a detecting plane, said sensor comprising a sensitive surface; - a light-emitting device for generating a luminous reference figure on said detecting plane, said light-emitting device comprising at least a first LED having a respective emission surface; - at least an objective having an optical axis through which a luminous radiation and a further luminous radiation pass, said luminous radiation coming from said object and being directed to said sensor and said further luminous radiation coming from said light-emitting device and being directed to said object, said luminous radiation defining between said detecting plane and said sensitive surface an optical path passing through said objective and said further luminous radiation defining between said detecting plane and said emission surface of said first LED a further optical path passing through said objective; - said sensor and said light-emitting device being positioned in such a way that, when said detecting plane is focused by said objective on said sensor, said sensitive surface of said sensor is on an image plane (60; 73) generated by said objective and said emission surface of said first LED is on a first plane which is a mirror plane with respect to said image plane (60; 73); - deflecting means (25, 26) comprising a first mirror interposed between said first LED and said objective arranged for deviating said further luminous radiation from said emission surface of said first LED and generating said mirror plane, characterized in that said light-emitting device comprises a second LED having a respective emission surface, said deflecting means (25, 26) comprising a second mirror interposed between said second LED and said objective arranged for deviating a further respective luminous radiation coming from said emission surfaces of said second LED such that said emission surface of said second LED is positioned on a second plane which is a mirror plane with respect to said image plane (60; 73), between said detecting plane and said emission surface of said second LED being defined a still further optical path passing through said objective such that a focusing condition of said detecting plane on said sensor corresponds to a focusing condition of said luminous reference figure on said detecting plane so that the focusing of said vision system is checkable during installation with the naked eye.