Patent ID: 7289271

Claim:
A tube lens unit, containing various focal lengths, with chromatically compensating effect for use with objectives of infinite image distance and chromatic residual errors, wherein the tube lens unit (TL) satisfies the following conditions: CHL=CHL o −A T 2 m T φ T =0 Equation (1) CHV=CHV o −1000 λm T φ T d 1 =0 Equation (2) where CHL is the longitudinal chromatic aberration of the combination of tube lens unit plus objective, CHL o is the longitudinal chromatic aberration of the objective, CHV is the chromatic difference of magnification of the combination of tube lens unit plus objective, CHV o is the chromatic difference of magnification of the objective, λ is the wavelength, m T is the dispersion index of the optical elements in the tube lens unit, derived from m T =m e =1/λν, in which e is the index of the main color and ν the Abbe number, A T is the radius of the exit pupil of the objective which is substantially equal to the entrance pupil of the lens unit, d 1 is the distance of the first optical element of the tube lens unit from the entrance pupil, φ T is the refractive power, and T is the index of the respective lens in the tube lens unit, A T 2 m T φ T =CHL T is the longitudinal chromatic aberration of the tube lens unit, and 1000λ e m T φ T d 1 =CHV T is the chromatic difference of magnification of the tube lens unit.