# 了解焦距与视场

### 固定焦距镜头

(1)$$\text{AFOV} \left[ ° \right] = 2 \times \tan ^{-1} { \left( \frac{h}{2f} \right)}$$

### 使用工作距离和视场来确定焦距

(2)\begin{align} \text{AFOV} \left[ ° \right] & = 2 \times \tan ^{-1} \left( \frac{\text{水平视场} \left[ \text{mm} \right] }{2 \, \times \, \text{WD} \left[ \text{mm} \right] } \right) \\ \\ \text{ or } \\ \\ \text{水平视场} \left[ \text{mm} \right] & = 2 \, \times \, \text{WD} \left[ \text{mm} \right] \times \tan \left( \frac{ \text{AFOV} \left[° \right] }{2} \right) \\ \end{align}
##### 图 2: 给定视场角下，HFOV、传感器尺寸与WD的关系。

(3)$$f = \left( \frac{h \, \times \, \text{WD} }{\text{水平视场}} \right)$$

### 使用具有固定放大倍率的镜头计算视场

(4)$$\text{水平视场} \left[ \text{mm} \right] = \frac{ \text{传感器水平尺寸} \left[ \text{mm} \right] }{\text{PMAG}}$$

(5)$${\text{PMAG}} = \frac{ \text{传感器水平尺寸} \left[ \text{mm} \right] }{\text{水平视场} \left[ \text{mm} \right] }$$

(6)$${\text{PMAG}} = \frac{\text{FL}}{\text{WD}}$$

(7)$$\text{水平视场} = \text{垂直视场} \, \times \, \text{宽高比}$$

## 镜头焦距示例

### 使用工作距离和视场来确定焦距

\begin{align} 2 \times \tan^{-1} \left( {\frac{50 \text{mm}}{2 \times 200 \text{mm}}} \right) & = \text{AFOV} \left[ ° \right] \\ \text{AFOV} & = 14.25° \end{align}

### 使用具有固定放大倍率的镜头计算视场

\begin{align} \text{PMAG} & = \frac{6.4 \text{mm}}{25 \text{mm}} \\ \text{PMAG} & = 0.256 \text{X} \\ \end{align}

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