CONTINUOUS SPHERICAL ABERRATION CORRECTION TUBE LENS

Tube lenses for imaging instruments are described herein. The tube lenses may be implemented with imaging instruments that include an objective lens that is not entirely infinitely corrected. A tube lens may include: a first optical element configured to receive diverging light from an objective lens along an optical path between the objective lens and the tube lens, and a second optical element. The first optical element converges the diverging light received from the objective lens onto the second optical element, and the first element is movable along its longitudinal axis relative to the second optical element.