Compound Light Microscope TOTAL MAGNIFICATION Power of the

Compound Light Microscope

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

Magnification Objective Ocular Total Eyepiece Magnification Low Power 4 x 10 x 40 x Medium Power 10 x 100 x High Power 40 x 10 x 400 x

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

Making cheek cell and onion cells slides • Cheek – 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

How does the FV change as Magnification goes Up? ? • As magnification goes up, the size of the FV gets smaller. • If magnification increases 2 x, the FV is divided by 2 x, or 2 x smaller. • If we switch from low power (4 X) to medium power (10 X), the increase in magnification is 2. 5 times (10 X/4 X). • 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 – 5 x; Med – 10 x; High – 50 x • Low FV = 5 mm (1000 um x 5 mm= 5000 um) • Step 1 – Calculate the increase in Magnification • Ex – 10 x/5 x = 2 • Step 2 – Calculate the reduction of the FV • 5000 um/2 = 2500 um