Adaptable operating frequency of a variable focal length lens in an adjustable magnification optical system

A non-transitory computer-readable storage medium storing instructions for operating an imaging system, the instructions when executed by a processor causing the processor to at least:

• determine that a variable magnification lens portion of the imaging system is in a first magnification state that provides a first magnification for the imaging system, the imaging system including a variable focal length lens portion comprising a variable focal length lens that provides a periodically modulated focal length that can be modulated at a first or second frequency that each provide a plurality of modulation periods during an image exposure period used by the imaging system and for which the first frequency is different than the second frequency;
• operate the variable focal length lens portion at the first frequency and a first modulation amplitude to provide a first range for the periodically modulated focal length of the variable focal length lens in response to the determination that the variable magnification lens portion is in the first magnification state, wherein the first range corresponds to a focus distance range of the imaging system during the first magnification state;
• determine that the variable magnification lens portion has changed to a second magnification state that provides a second magnification for the imaging system that is different than the first magnification;
• and
• operate the variable focal length lens portion at the second frequency and a second modulation amplitude to provide a second range for the periodically modulated focal length of the variable focal length lens in response to the determination that the variable magnification lens portion has changed to the second magnification state, wherein the second range is greater than the first range and corresponds to a focus distance range of the imaging system during the second magnification state.

A method for operating an imaging system used in a precision non-contact metrology system, the method comprising:

• providing an optical path for the imaging system, wherein the optical path comprises:
• a variable magnification lens portion that can be altered between a first magnification state that provides a relatively lower magnification for the imaging system and a second magnification state that provides a relatively higher magnification for the imaging system;
• and
• a variable focal length lens portion comprising a variable focal length lens that provides a periodically modulated focal length that can be modulated at a first or second frequency that each provide a plurality of modulation periods during an image exposure period used by the imaging system, wherein the first frequency is different than the second frequency;
• operating the variable focal length lens portion at the first frequency and a first modulation amplitude to provide a first range for the periodically modulated focal length of the variable focal length lens while the imaging system is operated using the first magnification state, wherein the first range corresponds to a focus distance range of the imaging system during the first magnification state, and
• operating the variable focal length lens portion at the second frequency and a second modulation amplitude to provide a second range for the periodically modulated focal length of the variable focal length lens while the imaging system is operated using the second magnification state, wherein the second range is greater than the first range, and corresponds to a focus distance range of the imaging system during the second magnification state.