Truevision Microscopes

Bringing your Microscope into Focus

The number markings on the lenses of your compound light microscope tell you how many times the object you are looking at would look bigger from the eyepiece. This is called the magnification. If you want to know the magnification of the object you are looking at, you need to check out the microscope lens. If your ocular or eyepiece lens is marked with the notation 10x, this means that all by itself, the objective lens is magnifying the objects ten times bigger than they really are. If you look at an object with your ocular lens and a low-power objective that is marked 4x, then the magnification of the object would be the magnification of your ocular lens multiplied by that of the objective. In this case, the object you are looking at would be forty times bigger than it actually is.

While magnification is an important thing when working with any type of microscope, you should also consider the resolution of the images you would be seeing through the ocular. A microscope with a high resolution would be able to pick out objects that are small and close together as separate objects. This means the resolution is defined as being able to distinguish two separate lines or objects as really two objects, and not one object.

Now that you know how your microscope objective lenses work, let’s get started looking at your slides and samples. There are some things you have to think about to avoid damaging your microscope objective lenses or your prepared slides. There are other things that are just good common practice for the care and use of the microscope. These things need to be known and remembered by the student microscopist. Below is the list for beginning students to remember.

1. Make sure that your microscope is set firmly on a table before your begin. Be careful in moving your microscope because some lamps and bulbs get hot after use. To avoid burning your hands, let your microscope cool down before moving it. Grasp the arm and the base firmly when moving the microscope. Do not carry it by the stage or the head. To increase bulb life, turn down the variable intensity before turning on the power to prevent the current rush on the cold bulb filament.

2. You can sit down in a chair or stool if you find that more comfortable than standing while looking through a microscope. Some microscopes have angled body tubes to make looking through the eyepieces easier. On others, the frame can incline.

3. To allow your eyes to adjust to the image seen through the ocular, start out with a low-power objective lens first. This will also help you focus your lenses on your sample as it is easier to focus using the low power objective than a high power objective since the high power objective lens has a small depth of field. Use the coarse adjustment knob so that the low power objective lenses are about an inch above the stage, then look through the eyepieces and keep adjusting the focusing until it is a clear image.

4. Use the stage clips carefully to secure the microscope slide on top of the stage. Make sure that the light under the stage is shining right through your slide. If you are using the mirror version of illumination source, never use your microscope in direct sunlight to avoid damaging your eyes with the reflected light from the mirror. When viewing thicker or bigger samples, you could turn on your lamp so that there would also be a light source on top of the microscope stage. This is called the incident light, or reflected light source. Some microscopes do not have lamps on the upper part, so you could use a normal table lamp or place your microscope in a brightly lit place. Generally, compound microscopes will not have any upper light. This however is typical for a low power stereo dissecting microscope.

5. Bring the stage closer to your objective lens by using the coarse adjustment knob. Check through the eyepiece to see if the slide is in focus. If it is, use the fine adjustment knob to focus clearly on your sample. Some microscopes have knobs to adjust the stage in the X and Y directions so you could focus your slide to the center of your field of view.

6. Looking through a high power objective will produce a larger image of the object you are viewing under a microscope. If you want to change this, just turn around the revolving nose piece and adjust to the objective you want to use.

7. Bring the low power objective lens back to focus before placing your microscope back to where it is stored. If there seems to be spots through the eyepiece, use only lens paper to clean the lenses of your microscope. Lens paper is available at camera stores. Normal cloth or tissue paper can damage your lenses. Keep in mind that dust can accumulate on the microscope eyepieces, the condenser below the stage, in the koehler field diaphragm below the stage, or even be on the objective lens itself.

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