Aberrations• Chromatic– is due to the fact that the refractive index of lenses, etc. varies with wavelength; therefore, focal lengths, imaging conditions, etc. are wavelength-dependent•Geometrical– are due to the deviation of non-paraxial rays from the approximations we have used so far to derive focal lengths, imaging conditions, etc.; therefore, rays going through imaging systems typically do not focus perfectly but instead scatter around the “paraxial” (or “Gaussian”) focusChromaticAberration(aka dispersion)Geometrical aberrationsPrimary (Seidel) aberrationsSpherical ComaAstigmatism Field curvatureDistortionSphericalComaSimultaneous compensationof spherical and coma,using the lens form factorfield curvatureastigmatismDistortionExact ray-tracingOptical designExact ray-tracingray scatter diagram ( ⇔ defocus)Optical designOptical design.........S4.........S30.11.0-21.6S20.0011.5421.6S10.11.0InfS0Distance to nextelementIndex to the rightCurvatureSurfacename10cm 10cm0.1cmFeatures of optical design software• Databases of common lenses and elements sold by vendors• Simulate aberrations and ray scatter diagrams for various points along the field of the system• Standard optical designs (e.g. achromatic doublet, Cooke triplet)• Permit optimization of design parameters (e.g. curvature of a particular surface or distance between two surfaces) vs designated functional requirements (e.g. field curvature and astigmatism coefficients)• Also account for diffraction by calculating the modulation transfer function (MTF)modulation transfer function (MTF)at different points along the fieldVendors• Optical design– Code V–Oslo– Zemax– Accos–Asap– consultants• Optics & opto-mechanics– Newport– Newfocus– Coherent– Opto-Sigma– Thorlabs– Edmund– specialized
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