Introduction to Microscopes
Purpose:
The Swift microscopes will be introduced. We will look at fibers and pigments.
Some Basic Rules About Using Microscopes:
1. Treat a microscope gently. Each one costs about $1200.
2. Always use both hands when carrying a microscope. Place one hand under the base (bottom) of the microscope after lifting the microscope by its arm..
3. Microscopes are good only if they are clean. Use only microscope lens cleaning paper to clean lenses, for the same reason as in rule 2: a single slight scratch can ruin the lens. NEVER wipe the lens using a circular motion; instead, tear a small piece of lens paper and sweep ONE TIME across the lens. Use a different piece of lens paper for each subsequent sweep, if necessary.
4. Whenever possible, hold the slide up to the light to identify the location of the specimen on it before placing it on the microscope stage.
5. To minimize eye fatigue, train yourself to keep both eyes open when looking through the ocular.
6. When drawing magnified specimens, always record the magnification at which the drawing was made. (The magnification of an object under the microscope is the product of the magnifications of the two lens systems, the objective and the ocular.)
7. When changing slides and when putting the microscope away, always have it with the scanning power lens down, i.e., the one with the lowest magnification, x4 in our case.
8. If you have trouble in seeing what you are looking for, ask the instructor for help!
Swift 3200M Compound Microscope
Introduction to the Swift 3200M Compound Microscope:
1. There are three objectives on the nosepiece, with magnifications of x4, x10, and x40. One usually starts with x4 objective because a larger area of the slide can be seen. (If you ever 'lose' something at a higher magnification, go back to x4, relocate the object, and then move to the next magnification.) To move to a different objective, rotate the circular metal nosepiece. Do NOT turn the nosepiece by using one of the objectives as a handle.
2. The ocular (eyepiece) has a built-in magnification of x10.
3. Some people find it useful to use the stage clips to clamp the slide. You can use one or both of the clamps. You can still move the slide around on the stage, but in a controlled fashion.
4. The stage is raised and lowered to bring an object into focus. When you start with a new slide:
a. Lower the stage and replace the slide,
b. Then, while looking at the microscope from the side, bring the stage up slowly as far as it will go without touching the slide. You do NOT want the objective to come in contact with the slide!
c. There are course and fine adjustments for the stage position. Often as you go from one objective to another you need to make a fine adjustment to the focus. The important point is that you make a habit of never raising the stage without being absolutely sure that it is safe.
5. The microscopes have an ocular micrometer on an arrow. The ocular can be rotated to orient the arrow in the direction you desire. To measure an object, the arrow and the object must be aligned. Sometimes both the object (or the slide containing the object) and ocular must be repositioned, as in the example to the right. |
|
A Little Practice:
The biggest problems for first-time users of microscopes are: getting the object you want to examine into the field of view, keeping it there, and focusing on it. Unfortunately these problems are interrelated. You need to be able to move the slide with one hand and focus with the other. Also you are seeing an inverted image, so that moving the slide to the right and toward you will move the image to the left and away from you.
1. Put the 'e' slide on the stage. Move the slide left, right, toward you, away from you. Look at the letter 'e' through the 4x objective. Then 10x, then 40x. Record brief observations.
2. Note that the arrow in the ocular has a micrometer scale. We will define each large division to be 1.0 ocular unit (o.u.). How large is each small division? How long is the arrow head? If the large marker is at 5.0 o.u., (and thus the inside of the arrowhead is at 0.0 o.u.), what is the location of the little dot? |
|
3. Estimate the width of the letter 'e' on the slide, i.e., the length of the crossbar. Pick the best objective, and record both the objective used and the length in o.u. Repeat for the thickness of the crossbar. Is a different objective better? Why? |
|
4. Look at the slide of the three colored fibers.
a. Use the 4x objective. Which fiber is on the top? the bottom? Draw a sketch.
As mentioned, focusing is a constant problem. With higher magnifications, you have a choice of exactly what to focus on. Our eyes have an extremely large depth-of-field, which means we can see, simultaneously, things close up and far away. On this microscope, the depth-of-field is fixed for a given objective. Thus, as you move the stage up or down you are bringing into focus different parallel planes in the object you are looking at.
b. Repeat step a.) using the 10x objective. Draw a sketch.
c. What is the width of a fiber? Record which objective you use and why? Record ocular units.
5. There is another slide with two pieces of some commercial printing.
a. Look at the sample on the left. How is the color produced?
b. Look at the sample on the right. How are the colors produced? Make a sketch. Describe patterns, sizes, spacings, and which objective.
Calibration:
The microscopes have an ocular micrometer. You may be asked to use a stage micrometer slide to calibrate the ocular micrometer, or your instructor may give you the calibration values. If you use the stage micrometer, draw/sketch the two scales to make clear what you see and measure. In either case you will have the conversion factor for each objective so that you can convert 'objective units', o.u., to micrometers, mm. Be sure to always record a size in o.u. and give the objective, then convert. Be sure to check your calibration with the instructor before going on.
Procedure for Each New Sample:
1. Obtain a slide containing the substance you want.
2. Examine dry sample and record your observations in a data table:
a. Appearance, shape, border: Sketches are appropriate! For pigments - (Apparent) color. How thick or definite is the border?
b. Size and objective: Using the eye-piece arrow micrometer, give the size or range of sizes. Also record which objective was used. Then you can convert to mm.
c. You will probably find that with the 40x objective there is not enough light to see well.
3. For the test with cross polarized light.
a. You need to be sure that one piece of the polarizing film is resting on the illuminator. This piece, called the polarizer, should just remain there for all the tests with the fibers.
b. The second piece of polarizing film, called the analyzer, needs to be brought into the field of view BETWEEN THE SAMPLE AND THE OBJECTIVE (the sample is between the two pieces of polarized film, like a sandwich).
c. Because of the small distance between the sample and the objectives, do NOT use the 40x objective with the cross polarization tests.
d. The plane of polarization of the analyzer must be perpendicular to the plane of polarization of the polarizer. As a check, if the two polarizing films are crossed, the light from a light source will not pass through the two filters. |
|
e. Record appearance and colors.
Knowns:
1. Look at 3 or 4 of the prepared Commercial Fibers. Use the list with the slides. Choose some that you think will be different from each other and then some that you might expect to be similar. Sketch. Measure. Comment. Compare and contrast.
2. We have prepared slides of pine (from our class - the first lab) and flax (the fibers Ms. Van Leeuwen prepared and that you used in the pulp painting). Samples were taken at different beating times. Look at one of each type, and then choose one of the types of fiber and look at the series of slides for that fiber. Sketch, measure, compare. What happens to the fibers as the beating time increased? How do the two fibers compare to each other?
Unknowns:
There are 4 unknowns. Select one or two. Record the letter identification of each unknown. Go through the same steps with each unknown that you did for the knowns. Record all observations in the same table.
Identify each of your unknowns. Write about one paragraph for each unknown explaining why you made the identification you did. Point out clues that might have confused you. If you have trouble choosing between two possible substances, give the characteristics that made you think of each substance but also why you chose the one you did. It is good science, when possible, to go back and look at the knowns again!
