Color-corrected optical system

A method, comprising:

• conducting polychromatic light through at least two optical members of a device, the optical members being located in an elongated tube configured for insertion into a body, wherein the members in combination are configured such that the device has an optical invariant-to-clear aperture semidiameter ratio greater than about 0.05, an optical path difference less than a value of the optical invariant divided by at least 250 times a midrange wavelength in a spectral range from about 435.8 to about 656.3 nanometers, wherein at least one of the optical members comprises an extraordinary dispersion optical material.

A device comprising:

• an elongated tube configured for insertion into a body;
• and at least two optical members located in the tube, wherein the optical members in combination are configured such that the device has an optical invariant-to-clear aperture semidiameter ratio greater than about 0.05, an optical path difference less than a value of the optical invariant divided by at least 250 times a midrange wavelength in a spectral range from about 435.8 to about 656.3 nanometers, and substantially corrects for chromatic aberrations throughout a spectral range from about 435.8 nm to about 656.3 nm.

A method comprising:

• conducting polychromatic light through at least two optical members of a device, the optical members being located in an elongated tube configured for insertion into a body, wherein the members in combination are configured such that the device has an optical invariant-to-clear aperture semidiameter ratio greater than about 0.05, an optical path difference less than a value of the optical invariant divided by at least 250 times a midrange wavelength in a spectral range from about 435.8 to about 656.3 nanometers, and substantially corrects for chromatic aberrations throughout a spectral range from about 435.8 nm to about 656.3 nm.