Cell Structure 57
LABORATORY
Cell Structure continued
EXERCISE:B. Magnification- The magnifying power of most objectives and
oculars is usually engraved. The ocu-lar lens
will be marked at the top edge. The
objectives- are engraved on the side of the
objective cylinder.^ - The low-power objective will be engraved
103, which means that the objective marked
will produce an image 10 times larger than
the object on the microscope slide.^ - When using a compound microscope, you are
using two sets of magnifiers. The ocu-lar lens
has a magnification of 103, and the lower
power objective has a magnifica-tion of 103.
Under low power, the objective forms an
image in the body tube 10 times larger than
the object on the microscope slide; the 103
ocular lens then magnifies that image another
10 times. Thus, the im-age that finally reaches
your eye has a total magnification of 100
times.
C. Using the Microscope- You are now ready to use the microscope, hav-
ing reviewed its parts. Be sure the microscope is
plugged into an electrical outlet; place the
microscope at your lab table with the oculars
toward you. Turn on the illuminator lamp. Clean
the ocular lens and the objectives with lens
paper provided by your instructor.^ - Get a microscope slide with a letter e and place
it on the stage over the stage opening. Be sure
your letter e covered with a cover slip is in the
center of the stage opening. Secure the slide
with the stage clips. Place the low-power ob-
jective in place. It will click and lock into posi-
tion. Lower the objective into place by turning
the coarse adjustment knob. Your microscope
should have an automatic stop, so you will not
crack the slide. Look through the eyepiece.
Notice the appearance of the letter e under low
power. Bring it into focus by slowly adjusting
the coarse adjustment knob by raising it above
the stopping point. Now look at the letter e on
your microscope slide. It is upside down but
when you look through the microscope it is
right side up. Now move the slide to the right;
the letter e moves to the left; now move the
slide to the left; the letter e moves to the right.
Move the slide away from you (up); the letter
e moves toward you (down). Move the slide
to-ward you (down); the letter e moves away
from you (up). These phenomena are called
inver-sions. Practice moving the slide around
to get^ used to the inversions.^- If you want to see more detail, you must
switch to the high-power objective. Using
your thumb and index finger, unlock the low-
power objective and move the high-power
objective into position by rotating the
nosepiece. Now use only the fine focus ad-
justment knob to bring that part of the letter e
you are viewing into focus. Notice how the
field of vision got smaller as the object to be
viewed got bigger. Your magnification now
under high power is 10 3 (ocular lens) 3 40 3
high{power objective 5 400. Remember- to
adjust the light if necessary.
D. Important Cautions- Use only the fine focus adjustment knob to
focus under high power; never use the coarse
adjustment knob under high power.^ - Use only lens paper to clean the ocular lens
and objectives; never use kimwipes or other
material. Other materials may scratch the
delicate lens. Always clean your lenses be-
fore lab and at the end of lab.^ - Keep the stage of the microscope dry at all
times to prevent corrosion of metal parts.
E. Depth of Focus- Get a microscope slide with three col-ored
threads mounted together. Under low power
(1003), focus where the three threads cross
one over another. Now us-ing the fine
adjustment knob, slowly focus