USE OF THE MICROSCOPE

Introductory information and care of the microscope:

• The microscopes used in this lab are monocular, compound, optical, bright-field microscopes.  They are designed to be parfocal; that is, if the microscope is clearly focused on a specimen with a lower power objective, it will be clearly focused (or very nearly so) when you swing the next highest objective into place.

   Procedure

• Position the microscope so that you can comfortably look through the ocular.  Adjust your chair height if necessary.
   
• See that the microscope is plugged into the outlet properly, with very little slack in the cord.
   
• Make sure the scanning (4X) objective is in operating position.  The scanning objective lens magnifies the image by a factor of 4, for a total of 40X.  (Total magnification is the product of the magnifications of each lens being used, that is, the ocular lens at 10X and, in this case, the scanning lens at 4X.)
   
• Obtain a prepared microscope slide (the newspaper "e" slide is a good one to start with).  You may also make a temporary slide with a small piece of newsprint (2-3 letters) and a drop of water between a clean glass slide and a cover slip.
   
• Use of the "e" slide demonstrates the "upside-down, reversed" image: as you move the slide to the left, the image goes to the right; as you move the slide away from you, the image moves toward you.  Also with the "e" slide you can learn to appreciate the concept of field of view, which lessens as you advance to higher magnifications.
   
• The total magnification achieved with the high power objective in position is ___________.
   
• You will examine "thread" slides to observe depth of field.  In this preparation, three different colors of thread were layered across each other.  As you attempt to focus, especially with 10X and 40X objectives, notice that you cannot get all threads in focus at the same time.  Even though the specimen on the slide appears thin enough to be two-dimensional, it does have thickness or depth.  It is a three-dimensional object.  Magnification emphasizes the thickness of the specimen.  Therefore, you see different levels come into clear focus as you slightly change focus.  This feature will be very important in understanding the position of cell components when studying tissue slides.

  Checklist for proper use of the microscope
 

• ALWAYS FOCUS WITH THE LOWEST POWER OBJECTIVE LENS FIRST, FOCUSING AWAY FROM THE SPECIMEN WITH THE COARSE ADJUSTMENT KNOB.
   
• CLARIFY THE FOCUS WITH THE FINE ADJUSTMENT KNOB IF NECESSARY.
   
• CENTER AN OBJECT OF INTEREST, THEN SWING THE NEXT OBJECTIVE LENS INTO PLACE AND ADJUST FOCUS WITH THE FINE ADJUSTMENT KNOB.  ADJUST THE LIGHT INTENSITY AS NECESSARY.
   
• CLEAN ALL LENSES WITH LENS PAPER BEFORE AND AFTER USE OF A MICROSCOPE FOR A LAB EXERCISE.
   
• PROTECT THE MICROSCOPE AS YOU RETURN IT TO ITS CABINET (CARRY IT CAREFULLY AND REPLACE ITS PLASTIC COVER).
   
• DO NOT DRAG THE MICROSCOPE ACROSS THE LAB TABLE.
   
• REPLACE PREPARED SLIDES IN THE PROPERLY MARKED TRAY.
   
• MAKE SKETCHES AS NECESSARY TO HELP YOU REMEMBER WHAT YOU HAVE SEEN.
   
• REPORT ANY DIFFICULTY OR MALFUNCTION TO THE INSTRUCTOR.
  
   

Checklist of parts of the microscope--please make sure you know the function and correct procedure for use of these structures:

        A.  ocular (magnifies 10X)
        B.  nosepiece
        C.  scanning objective (magnifies 4X)
        D.  low power objective (magnifies 10X)
        E.  high power objective (magnifies 40X)
        F.  coarse adjustment knob (use only with scanning or low power objectives)
        G.  fine adjustment knob (use with high power objective only)
        H.  iris (disc) diaphragm
        I.   stage platform with stage clips
        J.   light source/power source
        K  arm
        L.  base
       M.  body tube
       N.  condenser