(Adapted from http://www.biologycorner.com/) A microscope is an instrument that magnifies an object so that it may be seen by the observer. Because cells are usually too small to see with the naked eye, a microscope is an essential tool in the field of biology. In addition to magnification, microscopes also provide resolution, which is the ability to distinguish two nearby objects as separate. A combination of magnification and resolution is necessary to clearly view specimens under the microscope. The light microscope bends a beam of light at the specimen using a series of lenses to provide a clear image of the specimen to the observer. In this lab, parts of the microscope will be reviewed. Students will learn the proper use and care of the microscope and observe samples from pond water.
Your microscope has 4 objective lenses: Scanning (4x), Low (10x), High (40x), and Oil Immersion (100x). In this lab, you will not use the oil immersion lens; it is for viewing microorganisms and requires technical instructions not covered in this procedure. In addition to the objective lenses, the ocular lens (eyepiece) has a magnification. The total magnification is determined by multiplying the magnification of the ocular and objective lenses.
1. Plug your microscope into the power supply and switch on the illuminator. 2. Always start with the stage as low as possible and using scanning objective (4x). Odds are, you will be able to see something on this setting (sometimes it’s only a color). Use the coarse knob to focus: the image may be small at this magnification, but you won't be able to find it on the higher powers without this first step. Move the mechanical stage until your focused image is also centered. 3. Once you've focused using the scanning objective, switch to the low power objective (10x). Use the coarse knob to refocus and move the mechanical stage to re-center your image. Again, if you haven't focused on this level, you will not be able to move to the next level. 4. Now switch to the high power objective (40x). At this point, ONLY use the fine adjustment knob to focus specimens. 5. If the specimen is too light or too dark, try adjusting the diaphragm.
1. Store microscope with the scanning objective in place and the stage in its lowest position. 2. Wrap cords around the microscope. 3. Replace slides to original slide tray.
A large part of the learning process of microscopy is getting used to the orientation of images viewed through the oculars as opposed to with the naked eye. A common mistake is moving the mechanical stage the wrong way to find the specimen. This procedure is merely practice designed to make new users more comfortable with using the microscope.
This portion of the procedure is another practice to demonstrate depth perception. Many new microscope users find it difficult to conceive that the specimen on the slide is in three dimensions. As the stage is moved up and down, different threads will be in focus.
SEEING IS BELIEVING Microscopes that use visible light to view the microscopic world are broadly categorized as "light microscopes". Compound Microscopes are a type of light microscope that uses a series of 2 lenses in order to achieve higher magnifying power than simple microscopes having only one lens (also known as "dissecting microscopes".) When using a compound microscope, specimen must be placed on a transparent microscope slide and covered with a transparent cover slip in order to view. The specimen is then placed on the stage of the microscope over the light source to allow light to pass through the specimen. The illuminated specimen is viewed through 2 magnifying lenses; 1) the magnifying lens of the objective located on the rotating nose-piece which is positioned directly over the specimen, and 2) the magnifying lens located in the eye-pieces. The eyepieces have a fixed magnification of 10X. The rotating nosepiece will have an array of objectives ranging from 4X up to perhaps 100X, depending on the microscope. Each objective is clearly marked indicating its magnification power. The field of view DECREASES as you INCREASE magnification. You should notice that your DEPTH OF FOCUS decreases as magnification INCREASES. This means that with a relatively small movement of the fine focus knob, you could be out of the focal range. For looking at cells, you will notice you will see fewer layers of cells at higher magnifications. You can measure the actual length of your field of view by viewing a ruler or standardized grid with millimeter demarcations using the 10 X objective. count the number of mm in your field of view, then convert to micrometers. (1000um = 1mm).
The compound microscope allows us to magnify objects up to 1000 times (with a 100X objective). We can calculate the magnification we are observing with the microscope by multiplying the magnification power of the objective, by the magnification power of the eyepieces. The magnification of the eyepieces is always 10X. There fore, If you are using the 40X objective, the object you are viewing under the microscope would be magnified 400 times more than with the naked eye. If we do the math, we see that 10X times 40X equals 400X. Compound microscopes are good for viewing up to 1 micrometer, or 100 nanometers (nm).
I. HANDLING Before using the compound microscope, it is important to know how to handle and care for it. When transporting the microscope, it is very important to make sure that you have a good grip on the scope and carry it with 2 hands at all times. One hand should be placed on the base of the scope while the other should be placed on the body (see diagram). The scopes are not necessarily heavy, but their center of mass is at the base, making it unstable if supporting by one hand alone. You must also be sure that any cords are wrapped up and secured before supporting so as to not trip over the cord or create a hazard for others around you to possibly trip and fall. Skipping or overlooking any steps could result in very costly damage to the objectives, eyepieces or other microscopic parts. Please take care to read instruction first, before doing each and every step.
Can You Identify These Parts of The Microscope?
1) Turn off POWER switch. PARFOCAL The field of view DECREASES as you INCREASE magnification.The amount of light observed through the microscope gets dimmer (is reduced) as you increase magnification.You should notice that the image you see is UP-SIDE-DOWN and REVERSED (the is INVERSION).This means the object will appear to move in the OPPOSITE direct as it is being moved in reality.You should notice that your DEPTH OF FOCUS decreases as magnification INCREASES. This means that with a relatively small movement of the fine focus knob, you could be out of the focal range. For looking at cells, you will notice you will see fewer layers of cells at higher magnifications.You can measure the actual length of your field of view by viewing a ruler or standardized grid with millimeter demarcations using the 10 X objective. count the number of mm in your field of view, then convert to micrometers. (1000um = 1mm).
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