off-axis ellipsoidal mirror
离轴椭球镜

• rolling bearing
• rolling guide
• ROM masking
• ronchigram
• Ronchi grating
• Ronchi ruling
• Rontgen rays
• roof-angle
• roof-angle prism
• roof mirror
• roof photometer
• roof prism
• roof prisms
• roof top reflector
• room-temperature laser
• room utilization factor
• root angle
• root diameter
• root-mean-square
• root-mean-square deviation
• root-mean-square displacement
• root-mean-square error
• root-mean-square value
• rope pulley
• rosette method