Removing secondary spectrum in wide spectrum optical system

The partial dispersion of some typical glasses working on near infrared band was calculated with the formulas in which P and V were modified. The apochromatism of a wide band system was designed and analyzed. The result shows that the combination of the heavy crown glasses ZK8, ZK4 and special flint type TF3 is effective to correct secondary spectrum. Zonal chromatic aberration of the optical system is decreased from theoretic 0.18mm to 0.084mm in wide spectrum. The rear cut-off length of optical system is long enough for the reflector to image shifting compensation.