Lab for ISCI 2001
Care and Use of the Microscope

You will need to record data and answer questions for part of this lab

 

You will need to record data and answer questions for part of this lab.   All drawings must be labeled and include the magnification used.

Students will work with their lab partners. There will be 1 microscope for 2 people. It is assumed that you have read and know the various parts of the microscope and their functions.

RULES FOR MICROSCOPE USE: Always observe the following rules for microscope use:

  1. Always carry the microscope with two hands to your lab desk.
  2. The lowest power objective should be in position both at the beginning and end of microscope use.
  3. Use only lens paper for cleaning lenses.
  4. Do not tilt the microscope when viewing a wet mount.
  5. Keep the stage clean and dry to prevent rust and corrosion.
  6. Do not remove pats of the microscope.
  7. Report any malfunctioning.

Focusing the Microscope:

Lowest Power (Scanning) 4X

  1. Turn the nosepiece so that the lowest power lens is in straight alignment over the stage.
  2. Always begin focusing with the lowest power objective lens.
  3. With the coarse-adjustment knob, lower the stage until it stops.
  4. Place a slide of the letter e on the stage, and stabilize it with the clips or mechanical stage (instructor will demonstrate if necessary).
  5. Be sure that the lowest power objective is in place.  Then, as you look from the side, turn the coarse adjustment knob until the distance between the stage and the tip of the objective lens is no closer than 3 mm above the slide.
  6. While looking into the eyepiece, rotate the diaphragm (or diaphragm lever) to give the maximum amount of light.
  7. Slowly increase the distance between the stage and the objective lens, using the coarse-adjustment knob, until the object - in this case the letter e - comes into view, or focus.
  8. Once the object is seen, you may need to adjust the amount of light. Increase or decrease the contrast by rotatingthe diaphragm slightly.
  9. Use the fine-adjustment knob to sharpen the focus if necessary. Practice having both eyes open when looking through the eyepieces, as it greatly reduces eyestrain.

Higher Powers

Compound microscopes are parfocal; so that once an object is in focus with lowest power, it should be almost in focus with the higher power.

 

Bring the object into focus under the lowest power by following the instructions in the previous section.

 

Make sure that the letter e is centered in the field of the lowest objective. Move to the next higher objective (low power, 10x) by turning the nosepiece until you hear or feel it click into place.  Do not change the focus; parfocal microscope objectives will not hit normal slides when changing the focus if the lowest objective is initially in focus. If any adjustment is needed use only the fine-adjustment knob.  Always use only the fine-adjustment knob with higher powers.

 

Computing Total Magnification

 

When looking through the microscopes, you are actually viewing the specimen first through the ocular lenses and then through whatever objective is in place. In order to obtain the total magnification that you are viewing the specimen with you must multiply the magnification of

the ocular lens by the magnification of the objective.

 

Total magnification = Magnification of Objective x Magnification of Ocular

For example, if the ocular is 5x magnification and you are using the 10x objective, the total magnification would be 50x, i.e. the specimen would appear 50x larger than its actual size.

For the compound, it is the objective that is clicked into the vertical position above the light source.

 

Field of View (FOV)

 

The field of view (FOV) is the size of the circular area that you can see when you look through the ocular and objective lenses. Knowing the size of the FOV is important because you can use it to determine the approximate size of a specimen. The FOV will change as you change

the objective and therefore the magnification.

 

 

 

 

 

 

 

 

 

How to view a specimen:

 

For all specimens, use the following basic procedure.

 

1.) Clean the lenses of your microscopes if you have not done so already.

2.) Plug in your microscope and turn on the light source. You can experiment with how much light you allow using the dimmer, iris and condenser lens with the compound microscope. It is generally best

to start with a medium intensity of light and adjust accordingly. Keep in mind that the highest intensity of light is not necessarily the best for a given specimen.

Lab Exercise 1 - Letter "e" Lab

Supplies:

Standard Equipment Needed:

o                                Microscope 

o                                Pencil 

o                                Prepared letter "e"

o                                Paper containing "e" s 

o                                Scissors

Lab Procedure:

1. Using microscope, slide, cover slip, water, scissors, and newspaper make a wet-mount slide of a small-case letter "e".
2. Cut a small-case letter "e" from a newspaper.
3. Put the letter "e" on a microscope slide.
4. Using a dropper bottle, put a small drop of water on the letter "e".
5. Cover the letter "e" with a cover slip.
6. Look at the letter "e" using the low power objective lens.
7. What is the total magnification when using low power?
8. Draw what you see.
9. Rotate the nose piece to the medium power objective lens and observe the letter "e".
10. What is the total magnification when using medium power?
11. Draw what you see.
12. Rotate the nose piece to the high power objective lens and observe the letter "e".
13. What is the total magnification when using high power?
14. Draw what you see.

 

 

 

The letter"e" is a great way to learn how a microscope works. In this lab you will set up your microscope and view what a simple letter e cut out from a piece of paper looks like. First let's examine the letter "e" with your naked eye. Draw what you see in the circles below:

 

Follow these steps to use the microscope with a prepared slide:

o                                Place your letter "e" slide, coverslip side up, on the stage.

o                                Place the slide so that the letter is in its normal

o                                orientation in other words the way you would normally

o                                read it

o                                Use the low power objective.

o                                Secure the slide with the stage clips or mechanical stage.

o                                Turn on the light.

o                                Focus on the letter "e" using the coarse focusing knob. 

o                                Draw what you see in the circle below. Try using the high

o                                power objective. After focusing (fine focus only), draw what

o                                you see. 

 

 

Analysis Questions :

What are some of the ways the e you see with the microscope is different from the e you see with the hand lens?

If you are looking at the "e" through the microscope and you push your slide to the left, which way does the e in the microscope move? (Try this!)

If you push the slide away from you, which way does the e in the microscope move? (Try this!)

 

This phenomenon is known as inversion.

Total Magnification

Total magnification is calculated by multiplying the magnification of the ocular lens (eyepiece) by the magnification of the objective lens.

Exercise 2:

Calculate the total magnification for each objective, and record your figures in a table.  To calculate the total magnification, multiply the power of the ocular lens by the power of the objective lens.  Your table should include the powers of both lenses and the total magnification.

 

 

 

 

 

Microscope

Total Magnification

Value for each ocular unit (10X) at 4X (Scanning)

.

Value for each ocular unit (10X) at 10X (Low Power)

.

Value for each ocular unit (10X) at 40X (High Power)

.

 

Diameter of Field

The diameter of the field (the circle visible through the lens) is the length of the field across the center.

Exercise 3:

SCANNING (4x)

 

Place a clear plastic ruler across the stage so that the edge of the ruler is visible as a horizontal line along the diameter of the low-power field.  Be sure that you are looking at the millimeter side of the ruler.  You will use the ruler to measure the diameter of the field of view under various magnifications.

 

Estimate and record the number of millimeters (mm), to tenths, that you see along the field: (Hint: Start with one of the millimeter markers at the edge of the field.)

Convert the figure to micrometers (mm) and record.  This is your scanning diameter of field. To convert from millimeters to micrometers, multiply the millimeter value by 1,000.

Microscope

Field of View

Value for each ocular unit at 4X (Scanning)

.

Value for each ocular unit at 10X (Low Power)

.

Value for each ocular unit at 40X (High Power)

.


LOW POWER (10x) Repeat the steps above to determine (LPD)
HIGH POWER (40x) Repeat the steps above to determine (HPD)

Does low power or high power have a larger field of view and allow you to see more of the object?

Which has a smaller field but magnifies to a greater extent?

Reminder:

To locate small objects that are seen on low power, place these objects in the center of the field before rotating to high power.

Depth of Focus

The vertical distance that remains in focus at one time is called the depth of focus.

Constant use of the fine-adjustment knob when viewing a slide with high power will give you an idea of the specimen's three dimensional form.

 

There are a number of other items that can be viewed depending on time. These include human hair, human cheek cells, and red onion cells. Your instructor will demonstrate how to set up slides of each of these

 

 

 

http://www.umanitoba.ca/Biology/lab1/biolab1_6.html#

http://shs.westport.k12.ct.us/mjvl/biology/microscope/microscope.htm#wetmount