Laboratory 1: Measuring Field Size

Question 1

What’s the objective?

Answer 1

Students will calculate the field size (field of view) of a compound microscope at different magnifications and explore how magnification impacts the visible area.

Question 2

Materials (6)

Answer 2

• Compound microscope
• Stage micrometer (a slide with a precise scale etched onto it, usually in micrometers or millimeters)
• Prepared slides (e.g., onion cells, cheek cells, or other easily identifiable specimens)
• Calculator or Ruler (optional for manual measurements)
• Lens paper (for cleaning lenses)

Question 3

Parts in measuring field size (3)

Answer 3

• Part 1: Measuring the Field Size at Low Magnification
• Part 2: Calculating Field Size at Higher Magnifications
• Part 3: Observing a Specimen and Estimating Its Size

Question 4

Steps in Part 1: Measuring the Field Size at Low Magnification (4)

Answer 4

1. Set up the microscope by placing the stage micrometer on the stage and select the lowest objective lens (4x or 10x).
2. Focus the microscope by adjusting the coarse and fine knobs to focus on the etched scale of the stage micrometer.
3. Count the divisions that fit across the visible field, each division’s measurement (1 division = 0.01 mm), then multiply the number of divisions by the length of one division.
4. Record the calculated field diameter for the current magnification.

Question 5

Steps in Part 2: Calculating Field Size at Higher Magnifications (2)

Answer 5

1. Switch to a higher objective lens (40x or 100x) without moving the stage micrometer; remember that the field of view will be smaller at higher magnifications.
2. Calculate the field size for higher magnifications using the formula:
   Field size at higher magnification = (Field size at low magnification × Low magnification) / Higher magnification.

Question 6

Steps in Part 3: Observing a Specimen and Estimating Its Size (4)

Answer 6

1. Remove the stage micrometer and place a slide with biological material (like onion or cheek cells) on the stage.
2. Start with the lowest magnification to focus on the specimen, then switch to higher magnifications as needed.
3. Calculate the size of the specimen by dividing the field size at a certain magnification by the portion of the field that the specimen occupies.
4. Estimate the specimen size at various magnifications using the calculated field sizes for comparison.

Question 7

How does the field of view change as magnification increases?

Answer 7

As magnification increases, the field of view decreases. This happens because higher magnification lenses focus on a smaller portion of the specimen, reducing the visible area seen through the eyepiece. This phenomenon aligns with the basic principles of light microscopy, where higher magnifications offer more detail but limit the breadth of what can be observed (Burke, 2020).

Question 8

Why is it easier to measure the field size at lower magnifications than at higher magnifications?

Answer 8

Lower magnifications allow for a larger field of view. It is easier to align and count the divisions on the stage micrometer. It also requires less computational power and minor misalignments in the microscope setup or specimen can have less impact on the observed field size. At higher magnifications, the field of view decreases significantly, which makes it difficult to fit enough divisions to measure the diameter accurately and even small deviations can significantly alter the perceived field.

Question 9

How can knowing the field size help you estimate the size of an unknown specimen?

Answer 9

By knowing the field size, you can estimate the size of your specimen. First is to determine the size of the field, observe how many field units (divisions) the specimen occupies within the field of view, then plug into the equation: Specimen size Number of Field Units Occupied by Specimen/size of Field.

Question 10

Why is it important to know the exact field size when performing quantitative microscopy?

Answer 10

The exact field size or field of view (FOV) is crucial in quantitative microscopy because it precisely calculate the size, distance, or density of specimens. It also enhances reproducibility as it ensures measurements are consistent across different samples (Senft, et. al, 2023). Moreover, it helps understand spatial relationships and interactions between different structures within the specimen.