An optical device includes an elongated tube configured for insertion into a body and optical members located in the tube. The optical members are configured to have an optical invariant-to-clear aperture semidiameter ratio greater than about 0.05 and an optical path difference less than about a value of the optical invariant divided by at least 250 times a midrange wavelength in a spectral range from about 435.8 nm to about 656.3 nm, and are preferably formed of an extraordinary dispersion optical material. A method includes conducting polychromatic light through at least one optical member located in an elongated tube configured for insertion into a body, where the optical members have an optical invariant-to-clear aperture semidiameter ratio greater than about 0.05 and an optical path difference less than about a value of an optical invariant divided by at least 250 times the midrange wavelength from about 435.8 to about 656.3 nm.