extra central telescope
附加对中望远镜

• penetration frequency
• penetration of current
• penetraton depth
• penetrometer
• penetron
• penlight
• Penning effect
• Penning ionization
• Penning transfer
• pentaborate
• pentac lens
• pentaflex
• pentagon
• pentagonal aperture
• pentagonal prism
• pentagonal prisms
• penta mirror
• pentane
• pentane lamp
• pentaphosphate
• pentaprism
• penta reflector
• pentavalent
• pentode
• Pentovar lens