The present disclosure provides an optical imaging system with adjustable magnification. In one aspect, the optical imager, which defines an optical axis, includes an object plane and an image plane, an optical sub-system located along the optical axis and optically disposed between the object plane and the image plane, the optical sub-system being configured to substantially image electromagnetic radiation emanating from the object plane onto the image plane, and at least one detecting element located substantially at the image plane. In one example, the object plane and the image plane are separated by a fixed distance. In one example, the optical sub-system is configured to mechanically translate along the optical axis.