| A focus state reference subsystem (386) comprising a focus state reference object (388) and reference object optics (387) is for use in a variable focal length (VFL) lens system comprising a VFL lens (370), a controller (380) that modulates its optical power, and a camera (360) located along an imaging path including an objective lens and the VFL lens. The reference object optics (387) transmits image light from the focus state reference object (388) along a portion of the imaging path through the VFL lens (370) to the camera (360). Respective focus state reference regions (FSRRs) of the focus state reference object (388) include a contrast pattern fixed at respective focus positions relative to the eference object optics (387). A camera image that includes a best-focus image of a particular focus state reference region (FSRR) defines a best-focus reference state associated with that FSRR, wherein that best-focus reference state comprises a VFL optical power and/or effective focus position of the VFL lens system through the objective lens. |
