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How to use the microscope

Last updated on Monday, January 19 2009 by jdmiles

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A brief and basic review on the use of the microscope.

Many medical schools no longer require their students to learn how to use a microscope.  And yet, you may be in a pathology course where you are expected to look at microscope slides.  So here's a very brief crash course on the use of a microscope.

Nowadays, most microscopes look something like this:

The numbers in this image correspond to the following parts:

  1. Eyepieces
  2. Revolving nosepiece
  3. Objective lens
  4. Coarse focus knob
  5. Fine focus knob
  6. Stage
  7. Light source
  8. Condenser
  9. Stage adjustment



Add additional magnification, often 10X.  Most microscopes will have 2 eyepieces. Often, only one of these has a focus knob.  To get the other in focus, close one eye, look through the eyepiece that has no focus knob, and adjust the focus of the miscroscope using the fine and course focus knobs (4 and 5 in the image).  Then, focus the other eyepiece using the eyepiece's focus knob.


Revolving nosepiece

May have 3, 4 or more objective lenses, each with a different magnification (e.g., 4x, 10x, 100x).  Often, it is helpful to start with the nosepiece set to a low magnification when you first see the image, to scan it for areas of interest.  Then, dial up the magnification by rotating through the lenses in the nosepiece.


Objective lens

Magnifies the image.  In the microscope shown here, there are several objective lenses set into a revolving nosepiece, allowing for different strengths of magnification.

As an example, with your 4X objective lens in place, you'll get 40X magnification (the eyepiece also magnify, usually 10X).  Here's an example of a specimen viewed at 40x:

Dialing up the magnification with the revolving nosepiece, we get 100X magnification, which looks like this:

And dialing it up even further, to 200X, we see this:


Coarse focus knob

Twist this one way or the other to get the image approximately into focus.  Once you're pretty close, switch to the fine focus knob.


Fine focus knob

For very slight adjustments to the focus.  If your image is way out of focus, you're probably better off using the coarse focus knob until you the image is nearly focused.



This is where the specimen slide goes.  Place the part you want to look at over the hole in the center of the stage. 


Light source

Most microscopes in a medical school or residency setting will have variable light controls.  You can dial down the brightness when you're at low magnification, which will make it easier to see the specimen properly.  On the other hand, as you increase the magnification, you'll need more light to see well.



Even when the image is in focus, adjsuting the condenser can help sharpen the image.


Stage adjustment

Some microscopes have a pair of knobs that move the slide horizontally or vertically. This is sometimes easier than trying to move the slide with your hand.

There are doubtless some more detailed tutorials on the web.  If you find one, please leave a link in the comment box at the bottom of this page.