To look at blood cells you need to use the oil immersion objective
(100X). First focus on the objective using the scanning objective. Then move to
the 20X lens, refocus and then turn to the 40X objective and again use the fine
focus to sharpen the image.
Now move the high dry lens out of the way and place one drop of immersion
oil on the slide over the specimen. Swing the 100X objective into place so that
it goes into the oil. If you had the
slide in focus on 40X then the immersion oil objective won’t hit the slide but
it will get very close (parfocal). Use only the fine focus to bring the specimen
into sharpness with the 100X lens down.
You may move the slide about. The drop of oil is plenty for looking
around. When you are finished, wipe everything with oil on it off! You can
use Windex and Kleenex on the slide and use alcohol and lens paper on the oil
objective and the high dry objective.