Design of a double-telecentric machine vision lens with continuously adjustable magnification and low distortion

This paper proposes a design method for a double-telecentric machine vision lens with continuously adjustable magnification and low distortion. This applies the zoom principle, the optical focal power distribution condition, and the primary aberration theory of a paraxial optical system to study the solving method for the first-order optical parameters of the initial structure of the optical system, and then optimizes the aberration of the optical system. Finally, a double-telecentric machine vision lens with continuously adjustable magnification and low distortion is obtained, and the optical surfaces of all lenses are designed with a spherical surface. The working wavelength of the lens system is 400-700 nm, the working field of view of the object space is 27.5-18.34 mm, and a magnification ratio of -0.4× to -0.6× is obtained with the photo-detector of a 2/3 in. CCD. The radius of the root mean square of spot diagrams in the full field of view is less than 5.463 µm, and distortion is less than 0.18% in the variation range of the magnification ratio; and the value of the modulation transfer function is greater than 0.28 at the Nyquist frequency of 50 lp/mm, and it is essentially consistent with the diffraction limitation one. The double-telecentric machine vision lens with continuously adjustable magnification designed in this paper has good imaging quality and a reasonable structural design, which can meet the overall and local needs of observing objects at the same time and has good application value for the online detection of small-size defects in industrial production.