Field of View
• Field of View (FV) is the illuminated circle that you see when looking through the ocular eyepiece. • If we know the diameter of the FV then we can estimate the size of our microorganisms.
Field of View
• With our microscopes the diameter of the FV under low power is 4 mm
• FV is measured in micrometers or microns. • 1 mm = 1000 microns
• Therefore, our FV under low power is 4000 microns Using the Field of View to Estimate Microscopic Measurements
If an organism takes up ½ of the FV under low power, it must be about 2000 microns in length
How does the FV change as Magnification goes Up??
• As magnification goes up, the size of the FV gets smaller.
• If magnification increases 2x, the FV is divided by 2x, or 2x smaller.
• If we switch from low power (4X) to medium power (10X), the increase in magnification is 2.5 times (10X/4X). • The FV under medium power will be 1600 microns (4000/2.5)
Calculating the Diameter of the Field of View
Step 1 Calculate the Increase in Magnification. New Objective
Old Objective
Step 2 Divide the old F of V by the increase in magnification calculated in Step 1
Old F of V (Microns)
Increase in Mag
To Calculate the Changing FV
Low – 5x; Med – 10x; High – 50x
Low FV = 5mm (1000um x 5mm= 5000um)
Step 1 – Calculate the increase in Magnification
Ex – 10x/5x = 2
Step 2 – Calculate the reduction of the FV
5000um/2 = 2500um
Let’s try High Power
• Step 1­
• Step 2 – 50X
Microscope Measurements
1. A particular microscope has a total magnification at low power of 50x and a field of view of 6mm. Calculate the field of view at medium power with a total magnification of 100x. Your field of view should be expressed in microns.
2. A microscope has a total magnification at low power of 25x and a field of view of 5mm. Calculate the field of view at high power with a total magnification of 500x. Your field of view should be expressed in microns.
3. The following organisms were viewed using a microscope that had the following specifications (low power mag. of 30x and FOV of 6mm, medium power mag. of 90x, and high power mag. of 360x). Calculate the size of each organism in microns.
a)
90x
b) 360x