How to use a MicroscopeJanuary 19, 2010 at 4:27 AM | Posted in Grade Five Science | 19 Comments
Parts and Specifications
Historians credit the invention of the compound microscope to the Dutch spectacle maker, Zacharias Janssen, around the year 1590. The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope (vs./ an electron microscope). The simplest optical microscope is the magnifying glass and is good to about ten times (10X) magnification. The compound microscope has two systems of lenses for greater magnification, 1) the ocular, or eyepiece lens that one looks into and 2) the objective lens, or the lens closest to the object. Before purchasing or using a microscope, it is important to know the functions of each part.
Eyepiece Lens: the lens at the top that you look through. They are usually 10X or 15X power.
Tube: Connects the eyepiece to the objective lenses
Arm: Supports the tube and connects it to the base
Base: The bottom of the microscope, used for support
Illuminator: A steady light source (110 volts) used in place of a mirror. If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.
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.
Revolving Nosepiece or Turret: This is the part that holds two or more objective lenses and can be rotated to easily change power.
Objective Lenses: 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.
Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide. It is set at the factory and keeps students from cranking the high power objective lens down into the slide and breaking things. You would only need to adjust this if you were using very thin slides and you weren’t able to focus on the specimen at high power. (Tip: If you are using thin slides and can’t focus, rather than adjust the rack stop, place a clear glass slide under the original slide to raise it a bit higher)
Condenser Lens: The purpose of the condenser lens is to focus the light onto the specimen. Condenser lenses are most useful at the highest powers (400X and above). Microscopes with in stage condenser lenses render a sharper image than those with no lens (at 400X). If your microscope has a maximum power of 400X, you will get the maximum benefit by using a condenser lenses rated at 0.65 NA or greater. 0.65 NA condenser lenses may be mounted in the stage and work quite well. A big advantage to a stage mounted lens is that there is one less focusing item to deal with. If you go to 1000X then you should have a focusable condenser lens with an N.A. of 1.25 or greater. Most 1000X microscopes use 1.25 Abbe condenser lens systems. The Abbe condenser lens can be moved up and down. It is set very close to the slide at 1000X and moved further away at the lower powers.
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. There is no set rule regarding which setting to use for a particular power. Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use.
How to Focus Your Microscope: The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it. Now, look through the eyepiece lens and focus upward only until the image is sharp. If you can’t get it in focus, repeat the process again. Once the image is sharp with the low power lens, you should be able to simply click in the next power lens and do minor adjustments with the focus knob. If your microscope has a fine focus adjustment, turning it a bit should be all that’s necessary. Continue with subsequent objective lenses and fine focus each time.
1. eyepiece-where you look through to see the image of your specimen.
2. body tube-the long tube that holds the eyepiece and connects it to the objectives.
3. nosepiece-the rotating part of the microscope at the bottom of the body tube; it holds the objectives.
4. objective lenses-(low, medium, high, oil immersion) the microscope may have 2, 3 or more objectives attached to the nosepiece; they vary in length (the shortest is the lowest power or magnification; the longest is the highest power or magnification).
5. arm-part of the microscope that you carry the microscope with.
6. coarse adjustment knob-large, round knob on the side of the microscope used for focusing the specimen; it may move either the stage or the upper part of the microscope.
7. fine adjustment knob-small, round knob on the side of the microscope used to fine-tune the focus of your specimen after using the coarse adjustment knob.
8. stage-large, flat area under the objectives; it has a hole in it (see aperture) that allows light through; the specimen/slide is placed on the stage for viewing.
9. stage clips-shiny, clips on top of the stage which hold the slide in place.
10. aperture-the hole in the stage that allows light through for better viewing of the specimen.
11. diaphragm-controls the amount of light going through the aperture.
12. light or mirror-source of light usually found near the base of the microscope; the light source makes the specimen easier to see.
HOW TO USE A MICROSCOPE
All About Microscopes
You have recently obtained the position of Teaching Assistant to a professor of Sciences at the University of Brainiacs (U of B). Your job is to learn all there is to know about microscopes, before he will let you help him and the students. You must learn how the microscope became what it is today, starting with the invention and development and include drawings. Good luck in your search!
You are to create a folder using construction paper.
Inside the folder you will include information about Anton van Leeuwenhoek, a drawing of the microscope – which you will label and color, calculations of total magnification and how to make a temporary wet mount slide.
• Make a folder using a piece of construction paper.
Include the following items labeled A-E.
A• Using the links below, find and print a drawing of a microscope. Label this drawing with the correct terminology. Next, color YELLOW the parts of the microscope that light passes through, starting at the light source and ending at the eyepiece or ocular lens. Also, include the definition and job of each part of the microscope in your own words.
Do not print the definitions from the web page.
• Glue this drawing to the inside center part of the folder.
Include the word bank and definitions on the bottom of the page.
B• Using the links below, research Anton van Leeuwenhoek.
Write or type a complete and organized paragraph in your own words that includes the following information:
A. Who was Anton van Leeuwenhoek?
B. What are the dates of his birth and death?
C. Where was his homeland?
D. Why is he important?
E. Did he invent the microscope? If not, why is he credited with this invention?
C• Using the formula eyepiece X objective lens = total magnification,
calculate the following problems:
A. eyepiece= 10x objective lens= 40x
B. eyepiece= 5x objective lens= 10x
C. eyepiece= 20x objective lens= 20x
• Display these calculations on the right inside flap in a chart, only on the top half.
D• On the right inside flap (bottom half), describe how to set up a temporary wet mount slide. Use transition words to help the flow of your paragraph, and to avoid making it sound like a list.
E• On the outside front cover, label this folder THE MICROSCOPE and include your name and illustrations to enhance your project.
You will graded on each section as follows:
|labeling of picture||10 pts.|
|definitions of microscope parts||10 pts|
|coloring of light path||5 pts.|
|research of Leeuwenhoek||15 pts.|
|magnification calculations||15 pts.|
|description of a temporary
|overall neatness||10 pts.|
|followed all directions||10 pts|
|spelling and punctuation||5pts|
|on time||5 pts.|
Now, with all your new found knowledge on the microscope, you are on your way to becoming a full-time professor and helping to shape all those young minds at the U of B.
Resolution, Magnification, Penny