The optical system of the present invention comtemplates directing a beam of radiant energy to either an aperture beam splitter or polarizing beam splitter. Radiant energy from the beam splitter forms a first remote image at an entrance to an image scrambler so that any image information which the beam contains is destroyed. The output of the scrambler fills the full aperture of a focusing objective that reproduces the image of the output of the scrambler onto a sample. A mask, positioned at a remote image between the output of the scrambler and focusing objective, determines the geometrical shape of the sample image. The focusing objective images the radiant energy that is reflected from the sample to a second remote image at the scrambler so that the scrambler destroys image information while retaining spectroscopic information. The beam splitter reflects a portion of the radiant energy from the scrambler to the detector. The absence of image information in the radiant energy from the sample reduces measurement errors by producing a predictable dispersion of radiant energy at the detector.