Lateral chromatic aberration ($m(\lambda )$)

Lateral chromatic aberration, also called transverse chromatic aberration, is colour-dependent image scale: an object away from the optical axis can have different image heights at different wavelengths. Its changing transverse magnification produces displaced coloured edges. The on-axis parallel bundle in the chromatic aberration diagram illustrates axial chromatic aberration, and does not measure lateral chromatic aberration. ^[ref].