During 1970-1976 the field coalesced around practical phase retrieval by combining iterative two-image reconstruction, holographic sampling, and phase-based image alignment. Research pursued cross-disciplinary methods bridging optics, holography, electron microscopy, and early digital processing, prioritizing techniques capable of recovering phase information from intensity data or a small set of measurements. The era emphasized computationally tractable algorithms and demonstrations that could translate into laboratory practice and early hardware concepts.