Vision techniques used in automatic microassembly are limited by inherent problems such as small depth of focus and small field of view. Microassembly must, however, initially detect microparts in a wide field of view and large depth of field while maintaining high resolution. We propose microassembly using active zooming that can overcome these limitations. For a small field of view, active zooming prevents the target from getting out of the field of view during microassembly. For a small depth of focus, our proposal is based on focus measure to maintain clear target image in the field of view during microassembly. Two-step assembly thus ensures zoom microscopy maintaining a wide field of view and large depth of field initially and high resolution at the end. Peg-in-hole assembly experiments confirmed the feasibility of our proposal.