Question

For the following tip, explain the reasoning for why it should be followed.

When using a light microscope, focus the specimen with the scanning objective lens first
6. REASONING:

For the following tip, explain the reasoning for why it should be followed.

As you move up to the high power objective lens, avoid using the coarse focus knob.
7. Reasoning:

Answer 1

1) When using a light microscope, focus the specimen with the scanning objective lens first — Reasoning:

- The scanning (lowest-power) objective has the largest field of view and the greatest working distance, so it is easiest to find and center the specimen without losing it.
- Its larger depth of field and coarser focus tolerance mean you can bring the specimen into roughly correct focus quickly and safely.
- Starting with scanning minimizes the need for large focus changes when you rotate to higher-power objectives, reducing the chance of collision between the objective and the slide and making subsequent fine focusing faster and safer.

2) As you move up to the high power objective lens, avoid using the coarse focus knob — Reasoning:

- High-power objectives have a very short working distance and a much smaller depth of field, so large focus movements can very quickly drive the objective into the slide or coverslip.
- The coarse focus knob moves the stage (or objective) in large increments; using it at high power risks crashing and damaging the objective, the slide, or the specimen.
- The fine focus knob makes very small, precise adjustments appropriate for the sensitivity of high magnification and helps achieve sharp focus without overshoot.
- Many microscopes are parfocal: after focusing on low power you only need small fine adjustments on higher powers, so coarse focusing is unnecessary and unsafe.