The openness of following case has been allowed by our clients with exception of key parameters, which is only 90% of complete design process. I. Application The F - Theta is a file scanning device with optical system. II.Requirements Applicable wavelength: visible light File width: 14 in EFL: 24 in Lens quantity: no more than 5 pieces Lens facial form: all spherical Lens material: optical glass Scanning angle: 33.4 degrees Pupil diameter: 2.0 in Resolution: more than 25 lp/mm@0.3 III.Features F - θ lens have following features according to its basic performance: From the structure, deflection point position of beam light is equivalent to ordinary lens system aperture stop center, so f - θ lens system is asymmetric that its aperture stop center is in front of lens. From scanning process aspect, the collimating laser beam enter different field angle into entrance pupil, and then get light-spot through different f-θ positions in image plane.The effective angle of reflector is 2θ which is 2 to ordinary system. F - θ lens is an optical system with relatively small aperture while larger FOV. F - θ lens often requires the spot size from the edge to center is consistent. Due to small caliber, it is easy to adjust spherical aberration; while large FOV, there is higher demand for aberration adjustment for astigmatism and curvature of field. Usually, this scanning system only has monochromatic aberration while no chromatism as single laser light source which make optical material selection convinient. If need to adapt various laser light source system, it has to adjust chromatism. This design is to make optimization within visibal light range. In order to meet requirements of linear scanning, the system must have distortion. The propagation characteristics of laser beam which used as laser beam propagation is different from general beam, and  thus propagation characteristics of gauss beam in optical system must be considered (this design is for general beam). In general optical system, there is nonlinear tangent relationship between image height and field angle. F - Theta lens is optical system with big FOV and small relative aperture which needs to adjust aberration of axial point and off-axial. Since curvature of field is one of main factors interfere FOV to expand, there is much importantance to adjust it. The relative aperture of F-Theta is small, and minor spherical aberration and coma aberration, therefore, after introducing barrel distortion and adjusting field curvature, only astigmatism of monochromatic aberration need to be considered. IV.Results