A compound microscope displays magnified images of a specimen on a glass slide with a magnifying glass. Multiple lenses are used in the objective and the eyepiece to enlarge the image of a sample. It achieves this using two or more lenses in the objective and the eyepiece. In a microscope, the objective lens is located on the nosepiece and has a short focal length. It collects light from the target specimen and focuses the image on the microscope. Further enlarging the image is achieved with the second lens in the eyepiece, which has a longer focal length.
Origin of the compound microscope
The first compound microscope was invented in the late 1500s. The actual inventor is disputed because there were several people at work on them; Hans Lippershey (1570-1619), a German eyeglass maker, and the father and son team Hans and Zacharias Jensen. However, the father-son duo is usually credited.
The microscope was a handheld central cylinder with moveable eyepiece and objective tubes that produced a magnification of between three and nine times.
Parts of a compound microscope
- The ocular lens/eyepiece
- Nose piece or turret that holds multiple objective lenses
- Objective lens to magnify the images.
- The specimen is held in position by Stage Clips
- A Focus wheel to move the Stage
- The specimen is kept over the Stage
- A light source, light, or mirror
- Diaphragm or condenser lens
The function of a compound microscope
The primary source of light comes from the base of the microscope. The light passes from the base through the condenser and aperture, then through the contents of the Stage. The objective lens magnifies the image; the magnification power could vary from 4x to 100x. When the light reaches the eyepiece of the microscope, it is magnified by the ocular lenses; the magnification power could vary from 5x to 30x.
Common applications of a compound microscope
- The most important application of a compound microscope is using it as a biological microscope.
- A phase contrast microscope is a compound microscope used to observe blood cells and bacteria. These microscopes have a unique phase contrast objective lens and a phase slider that enhances the contrast in a sample without having to stain it.
- Another example is a polarising microscope used to cross-polarise the light and pick up differences in the colours in the optical path of the specimen being examined. A polarising compound microscope is often used in the pharmaceutical industry to examine chemicals and by petrologists and geologists to look at minerals.
- Metals, such as metals that cannot transmit light, are viewed under metallurgical microscopes in industrial settings. Darkfield microscopy is another technique that may be used in metallurgical microscopes as it involves back-illuminating the sample to highlight specific features such as hairline metal fractures and precious stone flaws.
- Fluorescence microscopes use different light wavelengths to fluoresce a sample to study the specimen.
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