Abstract: A viewing device to aid in authenticating an optical surface. The device includes a laser diode which produces a beam of light. The device includes a viewing screen which receives a diffracted image produced by the beam illuminating the surface. The device further includes a lens system which causes the diffracted beam to be focused on the viewing screen.

Abstract: A measuring instrument for reflectometric measurements, comprising a spherical measuring chamber (1) provided with a light source (2) and with a specimen aperture (3); a measuring channel (4) which has been provided with optics (5), with a photometer (6), with an optional stop (7) and with an optional filter (8); a reference channel (14) provided with optics (15), with a photometer (16), with an optional stop (17) and with an optional filter (18); and a signal processing and calculating device (20.sub.s, 20.sub.c) for processing and comparing with each other the light intensity values observed by means of the photometers in the measuring and reference channels. As taught by the invention, the measuring instrument comprises at least one visible light light source (2.sub.s) which emits substantially light having a wavelength mainly over about 380 nm, and a UV light source (2.sub.u) which emits substantially light in the UV range having a wavelength mainly under about 380 nm, advantageously 300 to 380 nm.

Abstract: An optical arrangement for a flow cytometer, wherein intense light is focused by a microscope objective having a numerical aperture Na.sub.i, onto the cells carried by a flow of water through the focal plane of the objective, with another microscope lens situated opposite the objective, with an optical axis and object plane coinciding with the objective and with a numerical aperture, NA.sub.O, which is significantly larger than that of the objective. The objective contains a circular field stop in, or close to, its secondary focal plane, with a diameter corresponding to a numerical aperture NA.sub.df, which is slightly larger than NA.sub.i, and much less than NA.sub.O. The fluorescence and scattered light from the stream of cells are separated by a dicroic mirror on basis of their different wavelength, so that they give rise to separate images in separate image planes of the objective.