The three‐dimensional imaging property and great depth of field immediately suggest applications such as population studies in large tanks. Less obvious applications based on optical filtering rather than imaging include diagnostic cytology and radiology.
Tiny variations in temperature, pressure and currents can be measured with modern electronics. Problems arise, though, when variations in one parameter affect the reading of another. Work on the Deep‐Sea Capsule has found some solutions.
Close inspection of spacecraft orbits has yielded a surprising amount of data on masses, radii, atmosphere and gravity of the moon and some planets and most recently lunar mascons.
Radio telescopes separated by many thousands of kilometers can be operated in pairs to obtain very high angular resolution, suitable for studies of quasars and hydroxyl‐line emitters, for geodesy, and for a test of general relativity.