Looking at Pond Water under a Student Microscope

What is a student compound microscope and what comprises the parts and functions? We will review the answers to this question in this article. A compound microscope has two or more lenses, thus the word “compound”, as it refers to compounding the magnification. The microscope eyepiece or ocular lens is the lens at the top on which your eye looks through. It makes the images from the objective lenses appear larger. These ocular lenses can generally magnify an image up to 10 or 15 times. The most common eyepiece is the 10x version. Holding the eyepiece is the body tube, the long tube that also acts as its support. The body tube is divided into the tube proper and the draw-tube. The draw-tube is the inner cylinder that increases or decreases the magnification of the object by varying the distance between the eyepiece and the objective cylinder. The body tube also carries the nosepiece and the objective lenses.

The nosepiece is rotating part at the bottom of the body tube. It also holds the objectives.
The objective lenses or objectives are where the rays of light from the object being examined first pass through. These are the lenses closest to the specimen being examined. Objectives come in a variety of powers. High-power objectives are long lenses that allow greater image magnification. Low-power objectives, on the other hand, have short lenses that have less powers of magnification. Some microscopes can have 2 or more objective lenses. These usually come in 4x, 10x, 40x and 100x labels, and sometimes have 20x and 63x as well. The 100x objective is usually an oil immersion objective meaning it requires a tiny drop of oil to be placed on the microscope slide for optimal viewing. This immersion oil has a refractive index close to the glass slide, allowing for less diffraction of light and better microscopic imaging.

The microscope stage is a flat platform on which the slides and samples are placed. Connecting the stage to the body tube is a curved metal piece called the arm. The arm (part of the vertical frame) is the most ideal part to hold when carrying the microscope.

There are stage clips that hold the glass slide into place. There are also movable stages that can be moved with movable jaws to location the specimen in the X and Y directions under the objective.

In the center of the stage, there is the aperture, or the hole that permits light to pass from the illuminator, or the light source. A mirror can be used to increase the light that shines through the specimen. An artificial light source can be used instead of a mirror. Sometimes artificial illumination from a halogen or incandescent microscope bulb requires the use of a color correcting filter lens to correct the light to look more light daylight. The common blue filter is often used for daylight color correction.

The amount of light passing through the stage can be adjusted with the use of the iris diaphragm. It can regulate the light that passes through it like that of a camera’s shutter. A reduced diaphragm opening will lessen the light that passes through the stage and will darken the image. It also increases depth of field when closing down an iris. However, not all microscopes have diaphragms. A cheap microscope or toy student microscope typically will not have these higher level options and features.

To focus the light from the microscope bulb (or mirror) onto the sample, a condenser lens is needed. Condenser lenses provide images that are sharper than those of ordinary lenses.

The large knob on the side of the microscope is the coarse adjustment knob. It is used to focus on the specimen by adjusting the position of the body tube. It should not, however, be used to focus when using high-power objectives as it can quickly damage the objective or prepared slide if the coarse focus is rapidly lowered and crashes the objective into the slide. The fine adjustment knob, on the other hand, is a small round knob that is used to make small adjustments on the microscope. It fine-tunes the focus of the specimen and is usually used after the coarse adjustment knob generally locates the objective to the approximate distance as needed for good optical focusing.

The base of the microscope is the bottom part that supports all the other parts of the microscope. Often, the microscope bulb as well as other parts such as the circuit board and power transformer are located inside the base. While different manufacturers and brands of student microscopes will vary somewhat, their basic parts and functions will remain the same. The student needs to familiarize himself with these features of the simple compound microscope as part of a well rounded education and introduction to the student microscope.