2 TOTAL MAGNIFICATIONPower of the eyepiece (10X) multiplied by objective lenses determines total magnification.
3 Magnification Objective Ocular Eyepiece Total Magnification Low Power 4 x10 x40 xMedium Power100 xHigh Power400 x
4 Field of ViewField 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.
5 Field of ViewWith our microscopes the diameter of the FV under low power is 4 mmFV is measured in micrometers or microns.1 mm = 1000 micronsTherefore, our FV under low power is 4000 microns
6 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
7 Making cheek cell and onion cells slides Scrape the inside of your cheek with a toothpickRub toothpick onto the slide and add a drop of methylene bluePlace a cover slip onto the slide. ObserveOnionPeel off inner epidermis of onion using forcepsPlace on slidePut a drop of iodine and a cover slip onto your slideObserve
8 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)
9 Calculating the Diameter of the Field of View Step 1 Calculate the Increase in Magnification New ObjectiveOld ObjectiveStep 2 Divide the old F of V by the increase in magnification calculated in Step 1Old F of V (Microns)Increase in Mag
10 To Calculate the Changing FV Low – 5x; Med – 10x; High – 50xLow FV = 5mm (1000um x 5mm= 5000um)Step 1 – Calculate the increase in MagnificationEx – 10x/5x = 2Step 2 – Calculate the reduction of the FV5000um/2 = 2500um