Steps to Focus a Microscope


Microscopes are tools that allow people to see extremely small things, including single-celled organisms and the makeup of plant matter. Students often use microscopes to see what they're reading about in science classes. Properly focusing a microscope can take some practice, but once you've learned how, it becomes second nature.


  • Prepare the microscope for use before focusing it. Set it on a flat surface, plug it in and place a glass slide holding a specimen (one that you prepared or one that was already prepared) on the stage. Make sure the lenses are pointed at the part of the slide you want to magnify and push the clamps over the slide. Once the slide is in place you're ready to start focusing on the specimen.

Objectives and Lights

  • Set your objective in place. The objectives are the long barrels that contain the lenses of the microscope, and there usually are three (short, medium and long barrels that step up in magnification from shortest to longest) that point down at the stage. Rotate the objectives so that when you look into the top of the barrel, you are looking down through the objective at the slide on top of the stage. Begin with the shortest objective and increase in power as needed to see the specimen.

    Adjust the iris at the same time you adjust the objective. The iris is an opening in the stage through which light travels. Adjust the amount of light by rotating a small knob. Once you have the proper amount of light and the right objective in place, you're ready to begin.


  • Turn the focus knob on the side of the microscope. Turning the knob away from you will lower the objective, while turning it toward you will raise it. Turn the knob very slowly because the difference between a perfect focus and a blurry one is no more than a fraction of an inch. Some microscopes have two knobs, one for coarse adjustment, another for fine adjustment. Once you have a specimen in a relatively clear view with the coarse adjustment knob, then turn the fine adjustment to perfect the focus.

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  • Photo Credit microscope image by Goran Bogicevic from
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