MooMooMath and Science

How to focus a microscope

Learn how to focus a basic compound microscope and open up a whole new microscopic world.

I have used a microscope in my Life Science class for over 15 years and have become an expert at focusing them.

Step 1. Place the prepared slide on the stage of the microscope. The stage contains clips that help secure the slide. I use these clips unless I'm focusing on pond water and then I don't use the slides so that I can move the slide around.

Step 2. Spin the nosepiece around until the lowest power lens clicks into place. Each lens is a different power and are labeled and have a different color. The lowest power will be the smallest lens. The low power lens is the easiest lens to focus. As you spin the nosepiece you should be able to feel the lens click into place. This makes sure that the lens is in the correct position.

How do you determine the magnification?
Multiply the ocular lens strength times the objective lens strength.
Look on the ocular lens to determine the strength or look in the manual. Most compound microscopes are 10x.

Each lens will also have the power magnification written on it. In this example I will use 40x.

10x times 40x = 400x

Step 3. Look through the ocular lens and use the coarse adjustment to begin to focus the microscope.
If the spicimen is dark or black you may need to turn on the power or adjust the light.

Step 4. When the specimen is close to be in focus you then can start using the fine adjustment to get the slide really clear and focused.

The coarse adjustment knob is usually larger than the fine adjustment.

Step 5. Use the diaphragm to adjust the light. The diaphragm is located under the stage and many people ignore this adjustment. It can make a big difference.