Measuring TechniquesD1

Part I: Part I:

Measuring the Size of a Specimen Measuring the Size of a Specimen Using the Field of View Technique.Using the Field of View Technique.

Preface: Before beginning this module, you should Before beginning this module, you should

be familiar with the parts, use, and care of be familiar with the parts, use, and care of the compound microscope.the compound microscope.

If you are unsure about the microscope’s If you are unsure about the microscope’s operation, please review the operation, please review the Use of the Use of the MicroscopeMicroscope module. module.

Mishandling of the microscope can lead to Mishandling of the microscope can lead to damage of the instrument.damage of the instrument.

Module Requirements: To complete this module, the following equipment will be To complete this module, the following equipment will be

provided to you by an SLC assistant.provided to you by an SLC assistant.

-microscope workstation-microscope workstation

-prepared microscope slide -prepared microscope slide

-stage micrometer-stage micrometer

-worksheet-worksheet

If materials are missing or you are having problems getting If materials are missing or you are having problems getting started, please ask one of the SLC staff for help.started, please ask one of the SLC staff for help.

Module D1: Objective

The completion of this module will allow The completion of this module will allow you to use the Field of View Technique in you to use the Field of View Technique in order to measure length, width, diameter order to measure length, width, diameter and other linear dimensions of a microscope and other linear dimensions of a microscope specimen.specimen.

Of all the microscope measuring techniques Of all the microscope measuring techniques covered at the Science Learning Center, the covered at the Science Learning Center, the Field of View Technique is the Field of View Technique is the least least preciseprecise..

Use the Field of View Technique only when Use the Field of View Technique only when approximate measurement is adequateapproximate measurement is adequate, and , and the specimen’s size is 30 to 4500 microns. the specimen’s size is 30 to 4500 microns.

Procedure:1. Chose the objective lens that is appropriate for your 1. Chose the objective lens that is appropriate for your

specimen. At this point, adjust your microscope, specimen. At this point, adjust your microscope, selecting the 10X objective lens.selecting the 10X objective lens.

Turn and lock into place

Procedure Continued:2. Obtain a stage micrometer. The Science Learning 2. Obtain a stage micrometer. The Science Learning

Center uses 2mm micrometers divided into units Center uses 2mm micrometers divided into units of 0.01 mm. of 0.01 mm.

Procedure Continued:3. Position the stage micrometer on the microscope’s stage and 3. Position the stage micrometer on the microscope’s stage and

clearly focus the scale using the 10X objective lens.clearly focus the scale using the 10X objective lens.Note: If you are having trouble finding the scale at 10X, switch to a lower power, such as 4X, to Note: If you are having trouble finding the scale at 10X, switch to a lower power, such as 4X, to

center scale. Then select the 10X objective and use the fine adjustment to focus.center scale. Then select the 10X objective and use the fine adjustment to focus.

Procedure Continued:4. Measure the diameter of the field of view.4. Measure the diameter of the field of view.

To make your measurement, line up one end of To make your measurement, line up one end of the stage micrometer scale with the edge of your the stage micrometer scale with the edge of your field of view. Adjust your microscope now.field of view. Adjust your microscope now.

Example

Procedure Continued: With the micrometer lined up in your field of view, With the micrometer lined up in your field of view,

measure the diameter to which your eye can see within the measure the diameter to which your eye can see within the illuminated area.illuminated area.

Note: At this point do not adjust your stage.Note: At this point do not adjust your stage.

Write down your measurement on a piece of scrap paper.Write down your measurement on a piece of scrap paper.

Procedure Continued: You should have found your workstation You should have found your workstation

microscope field of view to measure in a microscope field of view to measure in a range between 1.66 and 2.06 mm.range between 1.66 and 2.06 mm.

If your results are different, please go If your results are different, please go through the procedure again. through the procedure again.

If problems remain, please ask an SLC If problems remain, please ask an SLC representative for assistance.representative for assistance.

Notes: When we measured the field of view, we When we measured the field of view, we

took the diameter of the “circle” that we took the diameter of the “circle” that we could see using our microscope. That could see using our microscope. That distance may vary from scope to scope due distance may vary from scope to scope due to calibration, manufacture, and of course to calibration, manufacture, and of course human error.human error.

For this reason, we must include an For this reason, we must include an uncertainty with our measurement.uncertainty with our measurement.

Calculating the Uncertainty The uncertainty of your measurement can be given The uncertainty of your measurement can be given

as +/- one tenth (0.1) of the diameter of your field as +/- one tenth (0.1) of the diameter of your field of view measurement. of view measurement.

Example: My field of view measurement is 1.85 mm. So my uncertainty Example: My field of view measurement is 1.85 mm. So my uncertainty would equal +/- 0.185.would equal +/- 0.185.

Therefore, if the length of my specimen is Therefore, if the length of my specimen is 1.255mm and I have an uncertainty of 0.185. I 1.255mm and I have an uncertainty of 0.185. I can say that actually the specimen measures can say that actually the specimen measures between 1.070 mm and 1.440 mm. between 1.070 mm and 1.440 mm.

Try It!1.1. Remove the stage micrometer.Remove the stage micrometer.

2.2. Place your sample specimen on the stage.Place your sample specimen on the stage.

3.3. FocusFocus

4.4. Estimate the area covered by your specimen.Estimate the area covered by your specimen. For example, we have drawn imaginary lines across our field of view to

show that the size of this stone is 1/3 of our field of view.

Try It!5.5. Calculate the size of the specimen by multiplying the Calculate the size of the specimen by multiplying the

fraction of the field the specimen covers, times your fraction of the field the specimen covers, times your field of view. Don’t forget your uncertainty!field of view. Don’t forget your uncertainty!

For example: Our specimen covers 1/3 of the For example: Our specimen covers 1/3 of the field of view. The initial field of view field of view. The initial field of view measurement was 1.85 mm. The calculation measurement was 1.85 mm. The calculation would be:would be:

(0.333)x(1.85) = 0.617 mm +/- .185 mm(0.333)x(1.85) = 0.617 mm +/- .185 mm

Important If you change to a different objective lens, If you change to a different objective lens,

the field of view will be different than the the field of view will be different than the measurement you have taken for the 10X measurement you have taken for the 10X objective. objective.

Naturally, the field of view decreases with Naturally, the field of view decreases with greater magnification.greater magnification.

Therefore, if you must change the power of Therefore, if you must change the power of the objective lens, you must determine the the objective lens, you must determine the diameter of the new field of view.diameter of the new field of view.

Measurement Conversion In some cases you will be required to In some cases you will be required to

convert your measurements to a smaller convert your measurements to a smaller size.size.

A useful conversion to remember is A useful conversion to remember is millimeters (mm) to microns (millimeters (mm) to microns (μm)μm). .

1000 1000 μm = 1 mmμm = 1 mm1 1 μm = 0.001mmμm = 0.001mm

Measurement Conversion Let’s use our earlier example to perform a Let’s use our earlier example to perform a

measurement conversion. Our specimen covers ½ measurement conversion. Our specimen covers ½ of the field of view. Our initial field of view of the field of view. Our initial field of view measurement was 1.85 mm. Your calculation measurement was 1.85 mm. Your calculation was.was.

(0.5)x(1.85mm) = .925 mm +/- .185 mm(0.5)x(1.85mm) = .925 mm +/- .185 mm

(0.5)x(1850(0.5)x(1850μm) = 925 μm +/- 1.85 μmμm) = 925 μm +/- 1.85 μm

Note: do not forget to convert your uncertainty to get Note: do not forget to convert your uncertainty to get your final answer.your final answer.

Module Completed!

Please return to the main desk to obtain a Please return to the main desk to obtain a post test from your friendly Science post test from your friendly Science Learning Center personnel.Learning Center personnel.