If a student is using the 40x lens, what is the total magnification of the image being viewed?

(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.

	Magnification	Ocular Lens	Total Magnification
Scanning	4x	10x	40x
Low Power	10x	10x	100x
High Power	40x	10x	400x
Oil Immersion	100x	10x	1000x

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.

Compound microscope
Microscope slide with the letter “e”

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.

Compound microscope
Microscope slide with 3 threads

Compound microscope
Microscope slide
Coverslip
Transfer pipette
Pond water sample

Magnification:

Figuring Total Magnification

Magnifying Objects/ Focusing Image:

When viewing a slide through the microscope make sure that the stage is all the way down and the 4X scanning objective is locked into place.
Place the slide that you want to view over the aperture and gently move the stage clips over top of the slide to hold it into place.
Beginning with the 4X objective, looking through the eyepiece making sure to keep both eyes open (if you have trouble cover one eye with your hand) slowly move the stage upward using the coarse adjustment knob until the image becomes clear. This is the only time in the process that you will need to use the coarse adjustment knob. The microscopes that you will be using are parfocal, meaning that the image does not need to be radically focused when changing the magnification.
To magnify the image to the next level rotate the nosepiece to the 10X objective. While looking through the eyepiece focus the image into view using only the fine adjustment knob, this should only take a slight turn of the fine adjustment knob to complete this task.
To magnify the image to the next level rotate the nosepiece to the 40X objective. While looking through the eyepiece focus the image into view using only the fine adjustment knob, this should only take a slight turn of the fine adjustment knob to complete this task.

Total Magnification:

To figure the total magnification of an image that you are viewing through the microscope is really quite simple. To get the total magnification take the power of the objective (4X, 10X, 40x) and multiply by the power of the eyepiece, usually 10X.

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