Abstract: A coaxial wideband refractive optical system is disclosed which permits the use of high resolution optical sensors and transmitters in the visible energy wavelengths centered at 0.5 microns to the 12 microns wavelength in the infrared energy band. The system includes a front objective lens of wideband transmitting material such as, for example, ZnS, ZnSe, GaAs, TI-1173 glass or Ge followed by a beamsplitter and two doublet lenses. The front objective lens, which may be a positive lens, can have large color dispersion characteristics (aberrations) not normally associated with front lenses. A front, solid wideband objective lens is provided for receiving incoming electromagnetic energy radiating at about 0.5 micron to about 12 microns wavelength in the infrared for reducing the size of the beam diameter; thus, the size of the beamsplitter and the elements of the infrared and visible optical paths formed by the beam splitter may be reduced.