4/3" imagers are covered by TC and XC series lenses.
TC is short for Telecentric. Telecentric lenses have very low distortion and produce high-contrast images with high resolution in both the center and corners. Telecentric lenses have no change in magnification when focusing, and magnification is constant over working distances. These are ideal for precision measurement applications.
The XC lenses provide a large image format of Φ23mm for C-mount. These high-precision aspherical lenses significantly reduce distortion and produce high-definition pictures. XC lenses maintain megapixel resolution throughout the entire image, even if the iris is fully open.