Imaging lens check and active alignment method to maintain consistent rear focusing distance for an autofocus lens

A method of alignment assembly of an imaging system, the method comprising:

• positioning a lens holder at a calibrated back flange focal length from a calibration sensor, the calibration sensor disposed along an optical axis to receive an image thereon, the lens holder positioned along the optical axis and having a front aperture along the optical axis and a back flange along the optical axis, and the lens holder containing a front lens group disposed along the optical axis and a rear lens group disposed along the optical axis;
• translating, by an actuator, the front lens group to a plurality of positions along the optical axis, while maintaining the rear group in a fixed position relative to the calibration sensor, to change a focal distance to focus the image onto the calibration sensor;
• determining, by a processor, a calibrated position of the front lens group, the calibrated position being a position with a calibrated image focused at the calibration sensor;
• and
• setting, by the actuator, the front lens group to the calibrated position.