When focusing a specimen under a light microscope, you should always start with which objective lens?

• A. High power objective (40x)
• B. Oil immersion objective (100x)
• C. Low power objective (4x or 10x)
• D. Scanning objective (100x)

Answer: (C)

Verified step by step guidance

1. Understand the purpose of each objective lens on a light microscope: the scanning objective (usually 4x), low power objective (usually 10x), high power objective (usually 40x), and oil immersion objective (usually 100x).
2. Recognize that when initially focusing a specimen, you want a wide field of view to easily locate the area of interest on the slide.
3. Know that the scanning objective lens (4x) provides the widest field of view and lowest magnification, making it ideal for initially locating the specimen.
4. After locating the specimen with the scanning objective, you can switch to the low power objective (10x) to get a closer look and refine the focus.
5. Only after the specimen is centered and focused under low power should you move to higher magnifications like the high power (40x) or oil immersion (100x) objectives for detailed observation.