achromatically

Christiaan Huygens, another Dutchman, developed a simple 2-lens ocular system in the late 17th century that was achromatically corrected, and therefore a huge step forward in microscope development.

The instrument was an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that imaged the airglow limb through the interferometer.

Most photographic camera lenses are achromatically corrected to bring blue and red to a common focus - leaving large residual green and violet chromatic aberrations that degrades image sharpness; especially severe in long focus or telephoto lenses.