Focusing a Microscope

Exploring the Microscopic World

Discovering the hidden wonders of the microscopic realm through scientific exploration and observation.

Parts of a Compound Light Microscope

• Objective lenses: These lenses magnify the specimen.

• Eyepiece: Also known as the ocular lens, it further magnifies the image.

• Stage: The platform where the specimen is placed.

• Condenser: Focuses light onto the specimen.

• Light source: Provides illumination for the specimen.

• Diaphragm: Controls the amount of light on the specimen.

Microscope Illumination

Did you know that the diaphragm is responsible for regulating the amount of illumination to the specimen in a microscope? The condenser focuses and directs light onto the specimen, enhancing visibility. The diaphragm then allows a portion of that light to pass through. Without the condenser and diaphragm working together, observing microscopic details would be challenging.

Controlling Light with Diaphragm

The diaphragm is a mechanism in microscopes that controls the amount of light passing through the specimen. By adjusting the diaphragm, you can increase or decrease the brightness of the image. Use the diaphragm to optimize the lighting conditions for better visibility and contrast.

• Open the diaphragm for more light

• Close the diaphragm for less light

In figure (a) the diaphragm is 100% open allowing the most light through.

100% Open

In figure (b) the diaphragm is 80% open creating a less bright image.

80% Open

40% Open

In figure (c) the diaphragm is 40% open. This image is quite dark.

Multiple Choice

What part of the microscope determines the amount of light on the specimen?

• Objective lenses

• Eyepiece

• Diaphragm

• Condenser

Dropdown

​ Clarence wants to observe his specimen under the microscope but it is too dark to see any details. In order to better view his slide what does Clarence need to do?​

Select answer

Objective Lenses

• Objective lenses are used in microscopes to magnify the specimen.

• They are available in different magnification powers, such as 4x, 10x, 40x.

• Higher magnification lenses provide more detailed views of the specimen.

• Objective lenses are typically color-coded for easy identification.

​The paramecium in the 40x view are magnified by the low power lens (4x) and the eyepiece (10x). They appear 40 times bigger!

4 x 10= 40

40x

The paramecium in the 100x view are magnified by the medium power lens (10x) and the eyepiece (10x). They appear 100 times bigger!

10 x 10= 100

​​Sub header

The paramecium in the 400x view are magnified by the high power lens (40x) and the eyepiece (10x). They appear 400 times bigger!

40 x 10= 400

​​Sub header

Multiple Choice

What is the purpose of objective lenses in microscopes?

• To magnify the specimen

• To illuminate the specimen

• To rotate the specimen

• To clean the specimen

Match

Match the lens to its magnification power.

• Low Power Lens

• Medium Power Lens

• High Power Lens

• Ocular Lens
  (Eyepiece)

10x
(Objective Lens)

20x

40x

10x

• 10x
  (Objective Lens)

• 20x

• 40x

• 10x

Multiple Choice

What does the diaphragm control in microscopes?

• Amount of light passing through the specimen

• Magnification of the image

• Color of the specimen

• Size of the specimen

Maybe use headphones!

On the next slide you're going to watch a video about how to focus a microscope!

​Our microscopes are slightly different but that is OK! Observe how the scientist knows she is in focus!

Coarse Adjustment

• Coarse adjustment is used to roughly focus the microscope on the specimen.

• It is done by moving the stage up and down using the coarse adjustment knob.

• Be careful not to crash the objective lens into the slide as it may damage both.

Multiple Choice

What is coarse adjustment used for in a microscope?

• To roughly focus the microscope on the specimen

• To fine-tune the focus of the microscope

• To adjust the lighting of the microscope

• To clean the lenses of the microscope

Fine Adjustment

• The fine adjustment knob is used to fine tune your image.

• Typically, the fine adjustment knob will only be used in medium and high power magnification, as it moves the stage very slightly.

Multiple Choice

What is a fine adjustment knob used for in a microscope?

• To roughly focus the microscope on the specimen

• To fine-tune the focus of the microscope

• To adjust the lighting of the microscope

• To clean the lenses of the microscope

Steps for Focusing a Microscope

Step 1. Turn on your microscope and check that it is on the lowest power.
Step 2. Place the slide centered over the condenser, so that light shines through it.
Step 3. Slowly turn the coarse adjustment knob while looking through the eye piece until your specimen comes into focus.
Step 4. Turn the fine adjustment knob and diaphragm to adjust the image.

Drag and Drop

What are the correct steps for focusing your microscope?

Step 1. ​

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Step 2. ​ ​

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Step 3. ​

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Step 4. ​

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Step 5. ​

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Drag these tiles and drop them in the correct blank above

Turn on your microscope

Check that your microscope is on low power.

Place your slide above the light source.

Slowly turn the coarse knob to find the specimen.

Adjust with the diaphragm and fine adjustment

Now it is time to collect your microscope and slides in order to start investigating!

Good Work!