焦距计算器 — 公式
## Focal Length
The focal length defines the converging or diverging power of a lens or mirror.
### Formula
**1/f = 1/d_o + 1/d_i**
Lens power in diopters is **D = 1/f** (with f in meters). Positive focal length = converging lens; negative = diverging.
The focal length defines the converging or diverging power of a lens or mirror.
### Formula
**1/f = 1/d_o + 1/d_i**
Lens power in diopters is **D = 1/f** (with f in meters). Positive focal length = converging lens; negative = diverging.
计算示例
An object at 30 cm produces an image at 15 cm.
- 1/f = 1/do + 1/di
- 1/f = 1/30 + 1/15
- 1/f = 0.0333 + 0.0667 = 0.1
- f = 10 cm
- Power = 100/10 = 10 diopters