Which distance should the condenser be from the slide when viewing a blood smear?

• A. At the top of the slide
• B. In contact with the cover slip
• C. Midway between stage and slide
• D. 1-2 mm from top

Answer: (D)

When viewing a blood smear, you adjust illumination by controlling the condenser height so the light is concentrated onto the specimen. The condenser should sit very close to the slide—about 1–2 mm above the slide surface—so the light cone properly fills the field and passes through the cells. This distance gives bright, even illumination and good contrast, helping you distinguish individual blood cells. If the condenser is too close or touching the cover slip, glare can occur and you risk damaging the slide; if it’s too far away, illumination becomes uneven and dim. Hence, the practical setup is roughly 1–2 mm above the slide to optimize visibility.