Microscopes — Designation of microscope objectives — Part 1: Flatness of field/Plan

ISO 19012-1:2013 specifies the use of the marking "Plan" on microscope objectives, and defines the diameter of the sharp region of the primary image of a flat object surface. ISO 19012-1:2013 applies to visual observation using the combination of objective lens, tube lens and eyepiece, as specified by the manufacturer.

This marking is consistent with ISO 8578.