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**Compound Light Microscope**

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TOTAL MAGNIFICATION Power of the eyepiece (10X) multiplied by objective lenses determines total magnification.

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**Magnification Objective Ocular Eyepiece Total Magnification Low Power**

4 x 10 x 40 x Medium Power 100 x High Power 400 x

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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.

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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

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**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

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**Making cheek cell and onion cells slides**

Scrape the inside of your cheek with a toothpick Rub toothpick onto the slide and add a drop of methylene blue Place a cover slip onto the slide. Observe Onion Peel off inner epidermis of onion using forceps Place on slide Put a drop of iodine and a cover slip onto your slide Observe

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**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)

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**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

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**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

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