The authors propose an asymmetric stereo imaging system that acquires stereoscopic images through the installation of an additional small sub-camera module into a conventional single-lens digital camera. The small sub-camera offers advantages in the proposed system, such as reduced manufacturing cost and a reduction in hardware size. The proposed imaging system provides a practical configuration by considering the variations in focal length, which cause disagreement between the stereoscopic images. In order to resolve the disagreement problem, registration models are established to transform the asymmetric stereo images into symmetric stereo images. Experimental results confirm the accuracy of the registration algorithm and also show subjective evaluation of the images from the proposed system. Some applications of the proposed system, such as automatic horizontal image translation and a depth-based refocusing technique are implemented to show its practicality.