1. A microscopic imaging system comprising a receiving means for receiving an article to be imaged, a linear optical detector having a linear array of at least 2,000 pixels that extends in a first direction y, focussing means for focussing an image of an article in the receiving means onto the detector, scanning means for producing relative movement between the image and the detector in a second direction x that is substantially perpendicular to the first direction y, and an optical correcting element for reducing aberrations in the image focussed onto the detector, wherein the optical correcting element is astigmatic, and the dioptric power of the optical correcting element in the sagittal and tangential directions is defined by the functions D x =−Ay 2 /(B−Cy 2 ) and D y =g(y), wherein D x , and D y are the dioptric powers of the optical correcting element in the x and y directions, respectively; A, B, and C are coefficients. wherein B and C are not both zero; and g(y) is the general function of y.