An endoscope, comprising: a shaft comprising a proximal end and a distal end and a longitudinal axis spanning the proximal end and the distal end; an optical system disposed in the shaft, the optical system including an objective lens system (400, 900), and a first relay lens system (210' and 220'), the first relay lens system (210' and 220') consisting of two rod lenses (210', 220') arranged in a series, wherein each of the two rod lenses (210', 220') is a singlet, and wherein at least one of the two rod lenses (210', 220') is a diffractive/refractive hybrid singlet, and a single correction lens incorporated between the two rod lenses (210', 220'), wherein the correction lens is a doublet lens; and at least one additional relay lens system (210 and 220, 210" and 220") having two rod lenses (210, 220; 210", 220") arranged in a series, the at least one additional relay lens system (210 and 220, 210" and 220") arranged in series with the first relay lens system (210' and 220'), such that the number of relay lens systems of the optical system that have a correction lens including the first relay lens system (210' and 220') is less than or equal to the number of additional relay lens systems (210 and 220, 210" and 220") of the optical system, wherein the correction lens corrects aberration of the two or more relay lens systems (210 and 220, 210' and 220', 210" and 220"). a shaft comprising a proximal end and a distal end and a longitudinal axis spanning the proximal end and the distal end; an optical system disposed in the shaft, the optical system including an objective lens system (400, 900), and a first relay lens system (210' and 220'), the first relay lens system (210' and 220') consisting of two rod lenses (210', 220') arranged in a series, wherein each of the two rod lenses (210', 220') is a singlet, and wherein at least one of the two rod lenses (210', 220') is a diffractive/refractive hybrid singlet, and a single correction lens incorporated between the two rod lenses (210', 220'), wherein the correction lens is a doublet lens; and at least one additional relay lens system (210 and 220, 210" and 220") having two rod lenses (210, 220; 210", 220") arranged in a series, the at least one additional relay lens system (210 and 220, 210" and 220") arranged in series with the first relay lens system (210' and 220'), such that the number of relay lens systems of the optical system that have a correction lens including the first relay lens system (210' and 220') is less than or equal to the number of additional relay lens systems (210 and 220, 210" and 220") of the optical system, wherein the correction lens corrects aberration of the two or more relay lens systems (210 and 220, 210' and 220', 210" and 220"). an objective lens system (400, 900), and a first relay lens system (210' and 220'), the first relay lens system (210' and 220') consisting of two rod lenses (210', 220') arranged in a series, wherein each of the two rod lenses (210', 220') is a singlet, and wherein at least one of the two rod lenses (210', 220') is a diffractive/refractive hybrid singlet, and a single correction lens incorporated between the two rod lenses (210', 220'), wherein the correction lens is a doublet lens; and two rod lenses (210', 220') arranged in a series, wherein each of the two rod lenses (210', 220') is a singlet, and wherein at least one of the two rod lenses (210', 220') is a diffractive/refractive hybrid singlet, and a single correction lens incorporated between the two rod lenses (210', 220'), wherein the correction lens is a doublet lens; and at least one additional relay lens system (210 and 220, 210" and 220") having two rod lenses (210, 220; 210", 220") arranged in a series, the at least one additional relay lens system (210 and 220, 210" and 220") arranged in series with the first relay lens system (210' and 220'), such that the number of relay lens systems of the optical system that have a correction lens including the first relay lens system (210' and 220') is less than or equal to the number of additional relay lens systems (210 and 220, 210" and 220") of the optical system, wherein the correction lens corrects aberration of the two or more relay lens systems (210 and 220, 210' and 220', 210" and 220").