The resolving power of a microscope mainly depends on the numerical aperture.
This multiple-choice question tests a core concept in optics for exams like GATE Life Sciences.

The resolving power of a microscope determines its ability to distinguish two closely spaced points as separate, crucial for viewing fine details in cells or tissues. Governed by the formula d=0.61λNAd=NA0.61λ, where $d$ is the minimum resolvable distance, $\lambda$ is light wavelength, and NA (numerical aperture) is key, it mainly depends on numerical aperture.

Option Analysis

• Numerical aperture: Correct answer. NA = $n\sin \alpha$, where $n$ is refractive index and $\alpha$ is half the objective’s angular aperture. Higher NA (e.g., 1.4 in oil immersion) reduces $d$, improving resolution by gathering more light.

• Refractive index: Contributes to NA but not primary. It affects light bending (air n=1.0, oil n=1.51), enabling higher NA, yet resolution hinges on full NA value.

• Objective lens: Houses NA; its design sets max NA and aperture angle. Essential but resolution depends specifically on NA, not lens alone.

• Ocular lens: Provides magnification via eyepiece; does not affect resolution, which occurs at objective stage. Empty magnification worsens clarity if NA-limited.

Key Factors Table