Which of the following statements about oil immersion in light microscopy is correct?

• A. Oil immersion is primarily used to enhance contrast rather than resolution.
• B. Oil immersion decreases the numerical aperture of the objective lens.
• C. Oil immersion can be used at all magnification levels to increase resolution.
• D. Oil immersion is typically used only with the highest power objective lens to increase resolution.

Answer: (D)

Verified step by step guidance

1. Understand the purpose of oil immersion in light microscopy: it is used to increase the resolution of the image by reducing light refraction between the specimen and the objective lens.
2. Recall that oil immersion works by matching the refractive index of the immersion oil to that of the glass slide and the objective lens, which minimizes light bending and allows more light to enter the lens.
3. Recognize that oil immersion is typically used only with the highest power objective lenses (usually 100x) because at lower magnifications, the benefit to resolution is minimal and the technique is unnecessary.
4. Note that oil immersion does not primarily enhance contrast; contrast is usually improved by staining techniques or adjusting light intensity and diaphragm settings.
5. Understand that oil immersion actually increases the numerical aperture of the objective lens, which directly improves resolution, rather than decreasing it.