optically transparent meduim
光学透明媒质

• focal plane shift
• focal plane shutter
• focal plates, reticles
• focal point
• focal power
• focal ratio
• focal sphere
• focal spot
• focal surface
• focal zone
• focculation
• focimeter
• foco-collimator
• focoid
• focometer
• focometers
• focometry
• focon
• focus
• focus control
• focus drum
• focused
• focused beam
• focused condition
• focused energy weapon