Which objective focuses closest to the slide?
The correct answer and explanation is :
The objective that focuses closest to the slide is the oil immersion objective (usually 100x magnification).
Explanation:
A compound light microscope typically has multiple objective lenses:
- Scanning Objective (4x): Provides the widest field of view and lowest magnification, used for initial observation.
- Low-Power Objective (10x): Offers a closer view than 4x, commonly used for observing larger details.
- High-Power Objective (40x): Provides greater magnification for detailed examination of specimen structures.
- Oil Immersion Objective (100x): Requires a drop of immersion oil to eliminate air gaps, increasing resolution and focusing the closest to the slide.
The oil immersion objective focuses closest to the slide because:
- Shorter Working Distance: This is the space between the objective lens and the slide when the specimen is in focus. The 100x objective has an extremely short working distance, often less than 0.2 mm.
- Use of Immersion Oil: The oil immersion technique reduces light refraction by matching the refractive index of glass, ensuring clearer and sharper images. Without the oil, light bends away, reducing resolution.
- Maximum Magnification and Detail: The 100x objective allows for the highest possible magnification in a standard light microscope, making it ideal for observing bacteria, blood cells, and fine cellular structures.
Since the 100x oil immersion objective is designed to be as close as possible to the specimen while maintaining clarity, it is the correct answer to the question.