Back in the days of 35mm film, a 50mm prime was considered a 'standard' lens. That's because it gives pretty much the same perspective as viewing a scene with the human eye, without the magnification of a telephoto lens or the shrinkage a wide-angle lens uses to squeeze more into the frame.
The flexi disc (also known as a phonosheet or Soundsheet, a trademark) is a phonograph record made of a thin, flexible vinyl sheet with a molded-in spiral stylus groove, and is designed to be playable on a normal phonograph turntable.
Discs cushion the vertebrae, contribute to flexibility and help to protect the spinal cord. Discs are composed of a gel-like center (the nucleus pulposus) and a tough, fibrous outer layer (the annulus fibrosus). A herniated disc or bulging disc often is referred to colloquially as a slipped disc and a ruptured disc. No matter what you call them, these conditions can lead to nerve root irritation or impingement, which can cause traveling pain, numbness, tingling, muscle weakness and other disabling symptoms.