Microscope Measurement How big is that object in the microscope?

Calculating total magnification REVIEW If two lenses are always magnifying the specimen, how do you figure out the total magnification being used ? Total Magnification = ocular x objective = 10 x 4 (low power) = 40 (low power)

Try this one! If the ocular is 10x and the low power objective is 40x what is the total magnification? Then the total magnification under low power is 10 x 40 = 400x

Learning Goals Learn to calibrate a microscope. Use your microscope calibration to estimate the size of objects. Compound light microscope The microscopes at Auburn Drive have three objectives. Low Power (4x) Medium Power (10x) High Power (40x)

Field of View When you look into a microscope, the “field of view” is the visible circular area. If you change the objective, you change the magnification of the specimen. By knowing the size of the field of view (diameter), you can measure the size of objects in the microscope. Because the size of objects in the field of view is different at each magnification you have to calculate the diameters of the fields of view at each magnification. This process is called “calibrating your microscope”

Calibration Steps Place a ruler onto the microscope stage Record the diameter of the field of view in mm Change the objective to medium power, and record the measurement to the nearest mm Increase the magnification again. Notice that when you use the 40x magnification, the scale on the ruler is no longer visible. So how can we estimate the size of the field of view at 40x?

Calibrating with a ruler

My Calibration Chart 4 x 10 x 40 x Objective Measurement (mm) Micrometers (µm)

Estimating Specimen Size The area of the slide that you see when you look through a microscope is called the "Field of View".  If you know how wide your field of view is, you can estimate the size of things you see in the field of view. Figuring out the width of the field of view is easy - all you need is a thin metric ruler.

IMPORTANT FORMULA! Object Size = field of view (in mm) • 1000 number of “fits” Object Size = ? µm ** Remember that the field of view changes with each objective! If you are using objective 10 you must be sure to use a field of view of 2 mm.

Unit Conversions Millimeters is a nice metric unit, but when we use a MICROscope we tend to use MICROmeters.  Remember that there are 1000 micrometers (µm) in one millimeter. 1000 µm = 1 micron To convert from millimeters to micrometers, move the decimal 3 places to the right. 

Let’s try it out!

Tomorrow We will learn how to use and care for a microscope, beginning our studies into the micro-universe. Prelab Questions! Please copy & complete the following pre-lab questions before coming to class tomorrow! What kinds of safety concerns do you need to consider when you obtain and use a microscope? How do you think the orientation of an image seen with a microscope compares with the orientation of the actual specimen ? What is involved in recording your observations of microscopic specimens ?