Optics

Focal Length and Angle of View

• Formula: $\alpha = 2 \cdot \arctan \frac{d}{2f}$
• $\alpha$: Angle of view in radian
• $f$: Focal length
• $d$: Diameter. Regular 35mm film is 36mm wide and 24mm high, hence use $d=36$ for horizontal angle, $d=24$ for vertical.
• Popular focal lengths and horizontal angle of view
  1. 24mm: 74°
  2. 28mm: 65°
  3. 30mm: 62°
  4. 35mm: 54°
  5. 40mm: 48°
  6. 50mm: 40°
  7. 85mm: 23.9°
  8. 90mm: 22.6°
  9. 150mm: 13.7°
  10. 300mm: 6.87°
  11. 600mm: 3.44°