We have constructed a scanning Hall-probe microscope that combines a 1 X 4 cm scan range with 200 nm positioning resolution by coupling stepper motors to high-resolution drivers and reducing gears. The instrument is uniquely suited for efficient magnetic imaging of mesoscopic devices, media, and materials, operating from 4 K to room temperature with fast turn-around time. Its potential for studying dissipation in coated conductors--high-T_(c) superconducting tapes--is demonstrated via model systems. We image an entire sample of YBa_(2)Cu_(3)O_(7-delta), then zoom in to individual fluxons. Flux penetration into a single artificial grain boundary is imaged with 4 X 10~(-3) G/(Hz)~(1/2) field resolution and 25 (mu)s time resolution by averaging over cycles of ac driving current. Using the resulting magnetic movie, we map out ac power losses.
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