1. Magnification and Size
Measuring biological specimens using millimetres as units
SBI3U

2. Ocular lens (Eyepiece)
Body Tube
Nosepiece
Arm
Objectives
Stage
Stage Clips
Coarse Adjustment
Diaphragm
Fine Adjustment
Light
Always carry a microscope with one hand holding the arm and one hand under the base.
Base

3. What’s my power?
To calculate the power of magnification, multiply the power of the ocular lens by the power of the objective.
What are the powers of magnification for each of the objectives we have on our microscopes?

4. Field of View (FOV)
Field of View – the view you actually see when you look through a microscope

5. Low Field of View (Low FOV)
= measured with a ruler on the microscope
Count the spaces you see
Count the halves as well
Here we see 5.5 spaces
So Low FOV = 5.5 mm

6. Medium & High Field of View (FOV)
Medium FOV
= low FOV X _MagnificationLOW
MagnificationMEDIUM
High FOV
MagnificationHIGH
REMEMBER…we only use a ruler for LOW FOV

7. Let’s Practice
If the low FOV = 2mm, low magnification is 4x, medium magnification is 10x and high magnification is 40x, calculate the high FOV.

8. Let’s Practice
If the low FOV = 2mm, low magnification is 4x, medium magnification is 10x and high magnification is 40x, calculate the high FOV. High FOV = 2mm x _____4x___ 40x = 2 mm x 0.1 = 0.2 mm or 200µm

9. Let’s Practice
If the low FOV = 2mm, low magnification is 4x, medium magnification is 10x and high magnification is 40x, calculate the high FOV. High FOV = 2mm x _____4x___ 40x = 2 mm x 0.1 = 0.2 mm or 200µm

10. Specimen Size
You can estimate specimen size using the field of view. For example, if your field of view is 200 µm, and the specimen takes up about a quarter of the space, you can estimate it to be about 50 µm.

11. Drawing Magnification/Scale
When you are asked to draw what you see under the microscope, your drawings will be much larger than your specimen. You need to indicate approximately how much larger than life your drawings are.
Magnification = drawing size or M = D Actual size A

12. Drawing Magnification/Scale
e.g. a student, observing an amoeba under a magnification of 400X, calculates that it is about 50m long. If she then draws the amoeba 8 cm long, what is the magnification and scale of her drawing?
Magnification = drawing size = µm Actual size µm
= 1600 X, and the scale is 1cm = 6.25 µm.

13. To accurately measure the size of cellular structures we need a suitable scale:

14. Ideally, we need a scale we can see directly alongside the cells we are observing:

15. Start by putting a ruler under the microscope:

16. Appearance of ruler at medium magnification

17. Appearance of tissue at medium magnification

18. Estimating cell size at medium magnification12
1 mm
1mm / 12 cells = mm 5
1mm / 5cells=
0.2 mm
1 mm

19. Diameter of field of view/mm
Other units
Diameter of field of view/mm
No. of cells lengthways
No. of cells widthways
Mean length (mm)
Mean width (mm)
1.00 5 12
0.2
0.083
1mm = 1000µm
Mean length of cells = 0.2 x 1000 = 200µm
Mean width of cells = x 1000 = 83µm

21. Calculating actual size:

22. Calculating magnification & actual size:

23. Calculating actual size:

24. Calculating magnification:

25. Calculating magnification & actual size:

26. Calculating actual size:

27. Drawing Magnification/Scale
e.g. a student, observing an amoeba under a magnification of 400X, calculates that it is about 50m long. If she then draws the amoeba 8 cm long, what is the magnification and scale of her drawing?
Magnification = drawing size = µm Actual size µm
= 1600 X, and the scale is 1cm = 6.25 µm.