Online Lab Activity

onion cell at 40x magnification

Microscopy is the technical field of using microscopes to view samples or objects. The development of microscopes opened the field of science to a whole new dimension. Scientists discovered microorganisms, cellular structure, and the smallest parts of plants and animals on the planet, and more importantly, viruses. Dating as far back as 2600 b.c., rock crystal artifacts found in the shape of convex lenses were found. Over time, the progression for the use of lenses in scientific work continued until the late 1500's.

Zacharias and Hans Janssen are credited with the production of the first microscope around 1595. The first compound microscope had a 3x-9x magnification. Robert Hooke continued research on the initial premise and improved the compound microscope around1660. Anton Leeuwenhoek built a simple one lens microscope in during the late 1600's and early 1700's. They were reportedly the best in his time. In 1873, Ernst Leitz developed a microscope with a revolving nose piece for objectives. Max Knoll and Ernst Ruska built the first electron microscope in 1931 and 2 years later Ruska increased the magnification of the electron microscope to higher levels than the complound light microscope.

There are different types of microscopes: compound-light, dissection, scanning electron microscope (SEM), and transmission electron microscope (TES.) The compound light microscopes are light illuminated. The image seen with this type of microscope is two dimensional. This microscope is the most commonly used. You can view individual cells, even living ones. It has high magnification. However, it has a low resolution. A dissection microscope is light illuminated. The image that appears is three dimensional. It is used for dissection to get a better look at the larger specimen. You cannot see individual cells because it has a low magnification. SEM use electron illumination. The image is seen in 3-D. It has high magnification and high resolution. The specimen is coated in gold and the electrons bounce off to give you and exterior view of the specimen. The pictures are in black and white. TEM is electron illuminated. This gives a 2-D view. Thin slices of specimen are obtained. The electron beams pass through this. It has high magnification and high resolution.



fig.cox.miami.edu/.../light.microscope.gif


The parts of a microscope:

• Eyepiece
• Objectives
• Fine Adjustment Knob
• Power Switch
• Stage
• Diaphragm
• Base
• Body Tube
• Nosepiece
• Stage Clips
• Stage Stop
• Coarse Adjustment Knob
• Aperture
• Arm
• Light Source

To utilize a microscope you must first turn on the light and adjust the rheostat. The stage of the microscope is the area of the microscope where the slide is placed utilizing stage clips to hold the slide securely. The ocular housing is turned to select the magnification lens. The specimen is centered over the iris and the course adjustment knob is used to set the stage as high as it will go. You must adjust the oculars of the microscope while looking through them to view your specimen. The course focus knob is used while looking through the microscope on low power with the stage at the top until the image appears. The fine focus knob is used to clarify the image and the iris diaphragm to adjust the light. The objective lenses have different magnifications and the and the focus and iris diaphragm must be adjusted to compensate for the different magnifications. If the focus knobs and iris diaphragm are not utilized properly, the image quality will be poor, if the image is visible at all.