Tube lens unit with chromatically compensating effect

摘要

The invention relates to a tubular lens unit that obtains a chromatically compensating effect when used with objectives having an infinite image distance and chromatic residual errors. The inventive tubular lens unit fulfils the following conditions: equation (1) CHL=CHL_o-A_Tau² m_T ϕ_T=0, and equation (2) CHV=CHV_o-1000&1gr; m_T ϕ_T d₁=0, wherein CHL represents the chromatic longitudinal deviation of the tubular lens unit, CHL_o represents the chromatic longitudinal deviation of the objective, CHV represents the chromatic magnification difference of the tubular lens unit, CHV_o represents the chromatic magnification difference of the objective, &1gr; represents the wavelength, m_T represents the dispersion index of the tubular lens unit from m_Tau=m_e=1/&1gr;v wherein e is the main colour index, and &1gr; the Abbe number, A represents the field point, d₁ represents the distance between the first optical element of the tubular lens unit and the entrance pupil, ϕ_Tau represents the refractive power, and ϕ_T represents the index of the respective lens in the tubular lens unit.