1. The ratio of the focal length to the diameter of a (camera) lens system
   - focal ratio, f number, speed

Derived forms: stop numbers

Type of: ratio

• Raphicerus campestris
• Raphidae
• Raphidiidae
• Raphus
• Raphus cucullatus
• rapid
• Rapid City
• rapid climb
• rapid eye movement
• rapid eye movement sleep
• rapid growth
• rapid transit
• rapid-fire
• rapidity
• rapidly
• rapidness
• rapier
• rapine
• rapist
• Rappahannock
• Rappahannock River
• rapparee
• rappee
• rappel
• rappeller