flat-field objective
平场物镜，平扫描场物镜

• ultrawide angle lens
• ultrawide angle photographic lens system
• umber
• umbra
• Umen-second
• umweganregung
• unaberrated system
• unactivated
• unactivated state
• unadjusted eye
• unaided eye
• unannealed
• unbacked film
• unbalance
• unbalanced sight
• unbiased
• unblanking
• unblemished surface
• unblocking
• unbound electron
• uncertainty
• uncertainty condition
• uncertainty principle
• uncertainty relation
• uncharged particle