Objective for focusing

• A. 4x
• B. 10x
• C. 40x
• D. 100x

Answer: (B)

Focusing a specimen is easiest when you use an objective that gives a clear view with enough detail but still a reasonably broad field to keep the area you’re examining in frame. The tenfold objective does just that: it provides sufficient magnification to determine when the image is in sharp focus, while offering a wide enough view to center and adjust without quickly losing the specimen from sight. It also has a moderate depth of field, so you can bring the image into focus with the coarse knob and then fine-tune with the fine knob without chasing tiny changes.

Higher magnifications, like the high-power objectives, have very shallow depth of field and require extremely precise adjustments, making initial focusing much more challenging. The lowest magnification offers too little detail to judge sharpness quickly, whereas the tenfold objective strikes a practical balance, enabling reliable initial focus before moving to higher magnifications for more detail. After achieving a good focus at tenfold, you can switch to higher magnifications as needed, using fine focus to refine.