Optimized composition of two lenses, where one is made of dense flint and second of crown glass, assures much tighter focus than singlet spherical lenses due to minimized longitudinal and transverse spherical aberrations. They also feature nearly constant focal length across wide range of wavelengths.Cemented achromatic duplet lenses are optimized to provide excellent chromatic and spherical aberrations free performance. Standard achromatic duplet lenses cover two ranges – visible (400 nm – 700 nm) and near infrared (700 nm – 1050 nm).