D=0.61λ/N*sin（α/2）
D: Resolution
λ: The wavelength of the light source
α: Nose angle (the angle at which the specimen opens to the mouth of the objective lens at a point on the optical axis)
If you want to improve the resolution, you can by: 1. Reduce λ, such as using ultraviolet light as a light source; 2. Increase N, such as in cedar oil; 3. Increase the α, that is, reduce the distance between the objective lens and the specimen as much as possible