Entry Task
 Answer the following question on scratch paper &
hand in (5pts.):
If you look at the following slide under a
microscope (40x magnification), sketch the image
that you will see (does not have to be to scale)
e
Field of View (Update TOC)
 Learning Objective:
 I will determine the field of view width for
each magnification of the microscope and
use it to estimate the size of different cell
samples so that I can label my sketches with
a scale.
Field of View (Update TOC)
 Which is bigger? Can you tell?
What is missing???
Field of View (Update TOC)
 Which is bigger? You need a scale to tell!
Field of View
 The field of view is the circular area that is
visible when you look through the
microscope.
 It is difficult to know the size of the
objects that we view under the
microscope because we can’t measure
them with a ruler.
40x
What I am actually
looking at
100x
What I see through the microscope
400x
Field of View
 Size has to be measured indirectly, by
comparing the object to something we know
 the diameter of the field of view!
 Because the size of objects is different at each
magnification, you have to calculate the
diameters of the fields of view at each
magnification
 this is also called “calibrating your microscope”
40x
What I am actually
looking at
100x
What I see through the microscope
400x
Field of View
 As you change from the low power objective to the high
power objective, the field of view changes.
 As the magnification increases, the area that you are viewing
decreases. Magnification is inversely proportional to field of view
 In order to determine the size of the object that you are
viewing, you need to understand the scale that corresponds
to the magnification you are using.
 This is similar to zooming in on a map
 http://maps.live.com
Day 4: Determining Field of View
 Copy the table in your science notebook. (from page 257)
Eyepiece
Magnification
(a)
Objective
Magnification
(b)
4x
10x
40x
10x
10x
100x
40x
10x
400x
Total
Mag.
(𝒂 × 𝒃)
FOV
width
diameter
(mm)
FOV
FOV radius FOV radius
width
(mm)
(μm)
diameter
(μm)
 You will need this table to estimate the size of the cells that
you will be viewing in the next activities.
Measuring Field of View width for
the scanning objective (4X)
 We need to find the field-of-view width:
 using the scanning objective (4x), focus on
a clear millimeter ruler.
 Place the center of a whole number mark
on the left side of the field of view, making
sure that your ruler edge is exactly across
the center of the field.
Measuring Field of View width for
the scanning objective (4X)
 Count the number of lines that you
see in the field of view. (The
distance from the center of one line
to the center of the next line is
1mm.)
 This is the diameter of the field of
view for the scanning objective.
 Write this number in your table.
 Repeat for the Low Power
Objective (10x)
Calculating Field of View Width for the
high power (40x) objective
 Total Magnification of high power objective = 400x
 Total Magnification of scanning objective = 40x
400𝑥

40𝑥
= 10 The magnification increases by a factor of 10
decreases
 Therefore, the field-of-view width _____________
by a
factor of 10.
 Calculate the field of view width of the high power objective.
 Since the width is less than 1mm, we need to convert it to µmeters. (1mm = 1000 µ-meters)
Calculating the Field of View Width for
the low power (10x) objective
• Total Magnification of low power objective = 100x
• Total Magnification of scanning objective = 40x
•
100𝑥
40𝑥
= 2.5 The magnification increases by a factor of 2.5
decreases
• Therefore, the field-of-view width _____________
by a
factor of 2.5.
• Calculate the field of view width of the low power
objective.
• Convert it to µ-meters (1mm = 1000 µ-meters)
Field of View
 Finally, calculate the field-of-view radius for each
of the objectives.
 How can you use this table to estimate the size of cells
that you view?
 How can we estimate the size of our samples using the
microscope…
Field of View
 Finally, calculate the field-of-view radius for each
of the objectives.
 Now, we need to figure out how we can estimate the size
of our samples using this information…
Estimating the size of samples
 Work through the penny activity worksheet with
your partner.
 Make sure you show all your work, and sketch your
set-up.
 When you are finished, answer this question in your
science notebook: How can you use the FOV table
to estimate the size of something you view under
the microscope? Be specific in your answer.
 Homework: Measuring worksheet
Homework
Tomorrow we will start
looking at different types
of cells under the
microscope.