Microscope Lab

(Objective Lenses, image)



View of Cheek Cell, at 40x

According to the American Heritage Dictionary, a microscope is "an optical instrument that uses a lens or a combination of lenses to produce magnified images of small objects, especially of objects too small to be seen by the unaided eye."

( http://education.yahoo.com/reference/dictionary/entry/microscope )

The term "micro" means "small", and "scope" means "view".

http://www.southwestschools.org/jsfaculty/Microscopes/compoundscope.html

The first compound microscope was invented by Zacharias Janssen in 1595. Janssen's microscope was able to magnify an object 266x, whereas the modern microscope can magnify an object 1-2000x. This first microscope was improved by the work of Robert Hooke in 1660. Mr. Hooke was also responsible for coining the word "cell" and for discovering the role of oxygenation in the respiratory system. http://www.southwestschools.org/jsfaculty/Microscopes/fathers.html These men are responsible for the creation of this incredibly powerful instrument. There are four types of microscopes: compound, dissection, scanning electron microscope, and the transmission electron microscope.

The compound microscope is light illuminated ("light" refers to the method by which light transmits the image to the human eye), producing a 2-dimensional image. It is the most common of microscopes, allowing the viewer to see individual cells. "Compound" refers to the fact that the scope has more than one lens. It has high magnification, and low resolution. The second type is the dissection microscope. It is also light illuminated, but produces a 3-dimensional image. Because it is low magnification, one is not able to see cells. The third is the scanning electron microscope. It is electron illuminated with a 3-dimensional image. It is high magnitude, high resolution, but the picture is in black and white. The transmission electron microscope is also electron illuminated, but produces a 2-dimensional picture. You are able to view thin slices of specimen, and it is high magnitude, high resolution. http://www.southwestschools.org/jsfaculty/Microscopes/types.html

Parts of a Microscope:

Stage: "The flat platform where you place your slides. Stage clips hold the slides in place. If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs." One moves it left and right, the other moves it up and down. (http://www.microscope-microscope.org/basic/microscope-parts.htm) The stage helps to center the slide and focus it. It is best to look through the microscope while adjusting the stage.

Focus Knobs: The XY controls help to center the image in the slide bey turning them to move the stage forward and back, and side to side. There is also the Fine Focus Knob and and the Course Focus Knob. The course focus moves the stage rapidly. You should adjust it down until the image appears. The fine focus knob is a slow focus. It is best to be looking through the microscope while adjusting these knobs. (www.udel.edu/biology/ketcham/microscope/)

Iris: Diaphragm or Iris: "Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide." http://www.microscope- It is best to be looking through the microscope while adjusting the iris.

Oculars: "The lens at the top of the microscope that you look into. They are usually 10X but also are available in 5X, 15X and 20X. Widefield lenses have a large diameter and show a wide area of the field of view." http://www.nationaloptical.com/products/FAQ Oculars must be even to fit to the face, and it is suggested that you begin adjusting them by turning the right and left ocular to 64. This is best completed when looking at the microscope first, and then through it.(www.udel.edu/biology/ketcham/microscope/

Objectives: "Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4X, 10X, 40X and 100X powers. When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X , 400X and 1000X. To have good resolution at 1000X, you will need a relatively sophisticated microscope with an Abbe condenser. The shortest lens is the lowest power, the longest one is the lens with the greatest power. Lenses are color coded and if built to DIN standards are interchangeable between microscopes. The high power objective lenses are retractable (i.e. 40XR). This means that if they hit a slide, the end of the lens will push in (spring loaded) thereby protecting the lens and the slide. All quality microscopes have achromatic, parcentered, parfocal lenses." http://www.microscope-microscope.org/basic/microscope-parts.htm

In this day and age, we can hardly imagine life without microscopes. So much knowledge about cells and the human body has come from this irreplacable invention.