The development of formation flying technology in space has opened a new window for astronomy at hard X-γ-ray wavelenghts, allowing observations with unprecedented angular resolution (location accuracy of the order of few arcsec). This has stimulated the development of new concepts for imaging instruments: on one side, the focusing telescopes like γ-ray lens, using small,well shielded detector volumes, on the other side very large area γ-ray imagers, both allowing a big step in sensitivity. We report on a study for the concept of a large area (1 square meter), narrow field coded mask telescope with arcsec imaging capability, based on CZT detector technology and active collimation system, made of Si microstrip detector modules and operating in the energy band 15-500 keV. Feasibility and performance characteristics are discussed as well as possible geometric configurations and background suppression schemes, in the light of data obtained from INTEGRAL/IBIS and other CdTe/CZT instruments currently in space.