Objectives

1. Identification of Parts of Compound Light Microscope
2. Know about Resolution and Magnification of Light Microscope compared to the Naked Eye.

Anatomy of Compound Light Microscope

Parts and Usage of the Parts of Compound Light Microscope

• Ocular Lens / Eyepiece:- This is the part where the user keeps their eyes and observes the image of the sample.
• Revolving Nosepiece:- This part of the microscope helps the user to switch the magnification of the objective lens by switching the objective lens.
• Objective Lens:- This is the lens present near the sample in the Microscope. This is the part through which the light rays from the sample are observed.
• Stage:- The stage is where the prepared sample (slide) is kept to observe. The stage has a hole in the center (mostly) to let light from the light source to get to the sample.
• Slide Holder:- Slide Holders are there to keep the slide from moving after adjusting the microscope.
• Condenser:- Condenser helps to control the amount of light entering through the hole in the stage by limiting the amount of light passing through.
• Condenser Aperture Lever :- Lever to control the Condenser’s Aperture to aid its function.
• Light:- Light is there to illuminate the sample. A mirror to direct the light might also be found on some microscopes.
• Light intensity Control:- Controls the intensity of the light produced by the Light.
• Coarse Adjustment:- It is used to bring the specimen into approximate or "rough" focus when you first place a slide under the lowest-power objective lens.
• Fine Adjustment:- It is used to adjust the clarity of the image produced by the coarse adjustment by sharpening and focusing the image.
• Carrying Handle:- This is used to carry the Microscope the correct way.

Carrying the Microscope

This is the correct way of carrying the microscope.

Using the Compound Microscope Correctly

Microscope technique is the foundational skill for this experiment. The steps below are essential. Errors here will prevent you from identifying anything.

Step-by-Step Microscope Setup:

1. Start on the lowest objective (4x). Never place a slide under a high-power objective first. You risk cracking the slide and damaging the lens.
2. Place and secure the slide. Lay the slide flat on the stage, specimen-side up (a cover slip usually covers the specimen). Clip it in place. Centre the specimen over the aperture.
3. Use coarse focus only on 4x and 10x. Slowly raise the stage (or lower the objective) while watching from the side, then look through the eyepiece and focus upward.
4. Switch to 10x to locate your region of interest. Find a recognizable landmark (e.g. the outer edge of a stem section) before going higher.
5. Switch to 40x and use ONLY fine focus. Never use coarse focus at 40x. The working distance is tiny; you will crack the slide. If you need to use 100x magnification, these objectives need a drop of special oil (provided) on the slide; make sure to use it to see the clearest picture possible.
6. Adjust the condenser and diaphragm. Reduce the diaphragm aperture slightly to increase contrast. This is critical for seeing cell walls and internal layers.
7. Adjust illumination. Use the brightness control so the field is well-lit but not glaring. Washed-out images mean too much light; dark images mean too little.

Magnification and Resolution of Light Microscope

Magnification refers to the ratio of the apparent size of an object as seen through the microscope to its actual size. In a compound light microscope, magnification occurs in two distinct stages.

Total Magnification Formula can be written as

\(\text{M}_{\text{Total}} = \text{M}_{\text{Ocular Lens}} \times \text{M}_{\text{Objective Lens}}\)

Resolution is the minimum distance (d) between two distinct points at which they can still be distinguished as separate entities. A smaller value of d represents a higher resolving power.

The resolution of the Microscope is limited by the wave nature of the light.