Brightfield microscopes are among the most commonly used instruments in microbiology. This lesson introduces their major parts, explains how magnification and focusing work, and reviews practices that protect both the microscope and the specimen.
A brightfield microscope is a compound microscope: two or more lenses work together to magnify a specimen. It produces a darker image against a bright background. A microscope may be monocular, with one eyepiece, or binocular, with two. Each eyepiece contains an ocular lens, commonly magnifying 10×.
All flashcards
What is a compound microscope?
A microscope that uses two or more lenses, such as ocular and objective lenses, together to magnify an image.
How do you calculate total magnification?
Multiply ocular magnification by objective magnification. For example, a 10× ocular and a 40× objective produce 400× total magnification.
What do the condenser and diaphragm do?
The condenser focuses light on the specimen. The diaphragm regulates how much light reaches it.
When should coarse focus and fine focus be used?
Use coarse focus for large adjustments at low power, usually with 4× or 10× objectives. Use fine focus for small adjustments, especially at higher power.
Why is immersion oil used with an oil objective?
Oil reduces light scattering at the space between the specimen and lens because its refractive index is similar to glass. This increases the light collected and improves resolution.
Quiz questions
How is total magnification calculated on a compound microscope?Answer: Multiply the ocular magnification by the objective magnification.
Which control moves the slide horizontally across the stage?Answer: The x-y mechanical stage knobs.
How does darkfield microscopy produce a bright specimen against a dark background?Answer: It blocks direct light, allowing light refracted or reflected by the specimen to enter the objective.
Which statement distinguishes TEM from SEM?Answer: TEM uses electrons passing through a thin specimen; SEM scans the specimen's surface.
Why should coarse focus generally not be used with a 40× or higher objective?Answer: Its large movement can drive the objective into the slide and damage the slide or lens.
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.