The method for doing this is called köhler

The method for doing this is called Köhler
illumination.
Results in an evenly illuminated field and a
bright image without glare.
Achieved by adjusting the height of the
condenser (and closing the field diaphragm):
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Condenser Knob moves the
condenser up or down to control the
lighting focus on the specimen.
Field Diaphragm
Controls the diameter of the light
beam before it enters the condenser
aperture
Focus specimen. Close field diaphragm. Adjust height of condenser until leaves
of the field diaphragm are in sharp focus. Use the condenser centering screws to
move the image of the field diaphragm to the center. Open field diaphragm.
Setting Köhler

2.4, 2.5, 2.6 Measuring size
The ocular reticle is found in the ocular and is a
arbitrary ruler that can be used to measure
objects.
Must first be calibrated with a stage micrometer .
Must do this for each objective .
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Reticle Units
Let’s say that you determine
there are 40 reticle units per
millimeter.
How many µm are there per r.u.?
Remember that 1000 µm = 1 mm
So there are 40 r.u. per 1000 µm.
So 1 r.u. = 25 µm

For a particular microscope one reticle unit represents 25
µm when using the 4X objective. You want to know the
number of µm’s per r.u. when using the 40X objective on
the same microscope.
An equation: µm/r.u. x (Mag. of original objective /Mag.
of new objective) = µm/r.u.
a. 250 µm
b. 25µm
c. 2.5 µm
d. .25 µm

Paramecia (protist) and Elodea (plant)
What do you know about the structure and function of these
types of organisms?
What might they have in common? What are their
differences?

2.7 Living Specimens (Fun!)
In this section you will learn how to prepare a wet mount slide and
study the structure and function of these organisms (and others)
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Make sure to use your notebook for observations. You’ll examine a
variety of specimens including:
Living Paramecia :