Which objective uses the fine focus knob exclusively?

Which objective uses the fine focus knob exclusively?

• A. 4x
• B. 10x
• C. 100x
• D. 40x

Answer: (D)

Focusing becomes very precise as magnification increases. The coarse focus knob moves the stage in larger steps, which is fine for quickly bringing a specimen into approximate focus at low magnifications. But at higher magnifications the depth of field is extremely shallow, so big, coarse moves can overshoot or cause the objective to bump the slide. That’s why you switch to the fine focus knob for small, exact adjustments to bring the image into sharp focus. Because of this precision need, the higher-magnification objective is the one for which focusing is done exclusively with the fine adjustment. The lower-magnification objectives are typically focused first with coarse adjustment and then fine-tuned as needed.

Focusing becomes very precise as magnification increases. The coarse focus knob moves the stage in larger steps, which is fine for quickly bringing a specimen into approximate focus at low magnifications. But at higher magnifications the depth of field is extremely shallow, so big, coarse moves can overshoot or cause the objective to bump the slide. That’s why you switch to the fine focus knob for small, exact adjustments to bring the image into sharp focus. Because of this precision need, the higher-magnification objective is the one for which focusing is done exclusively with the fine adjustment. The lower-magnification objectives are typically focused first with coarse adjustment and then fine-tuned as needed.