In an eye-piece, field lens and eye lens have focal lengths 7.5 cm and 7.3 cm. To eliminate spherical aberration, distance between them would be

Options

A. 0.2 cm
B. 0.4 cm
C. 0.1 cm
D. 0.5 cm

Explanation

To solve the problem of determining the distance between the field lens and the eye lens in an eyepiece to eliminate spherical aberration, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Focal Lengths**:
- The focal length of the field lens (F1) is given as 7.5 cm.
- The focal length of the eye lens (F2) is given as 7.3 cm.

2. **Understanding Spherical Aberration**:
- Spherical aberration occurs when light rays that strike a lens near its edge focus at different points than those that strike near the center. This leads to a blurred image.
- To minimize spherical aberration, the distance (D) between the two lenses should be adjusted based on their focal lengths.

3. **Calculate the Distance**:
- The formula to eliminate spherical aberration is given by:
\[ D = F1 - F2 \]
- Substituting the values:
\[ D = 7.5 \, \text{cm} - 7.3 \, \text{cm} = 0.2 \, \text{cm} \]

4. **Conclusion**:
- The distance between the field lens and the eye lens to eliminate spherical aberration is 0.2 cm.

### Final Answer:
The distance between the field lens and the eye lens should be **0.2 cm**.

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