American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which type of objective provides the greatest depth of field and field of view?

1. Medium power

2. High power

3. Low power

4. Oil immersion

The correct answer is: Low power

The low power objective provides the greatest depth of field and field of view among the choices. This is primarily because the low power objective has a lower magnification compared to the other objectives, which allows for a broader area to be in focus at any given time. When using low power, it is easier to see a larger portion of the specimen because it magnifies less and captures more of the overall image, creating a wider field of view. Additionally, the depth of field—the vertical range or thickness of the specimen that remains in focus—also increases with lower magnification. This is especially advantageous when initially locating and viewing specimens, as it allows for a more comprehensive overview of the cellular structures and arrangements without the need for frequent adjustments to bring them into focus. In contrast, higher magnification objectives such as medium power, high power, or oil immersion provide a narrower field of view and shallower depth of field. As magnification increases, the area in focus decreases, making it harder to see the entire structure at once and requiring more careful focusing techniques. This is crucial in advanced microscopy techniques but is not optimal for initial examinations or when a broad perspective is needed.