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Using a Bright Field Light Microscope

Author(s): David R. Caprette, PhD

Adjusting the Oculars

You may not need your eyeglasses when using a microscope, unless they correct for astigmatism. Using a single ocular, the focus control alone can bring an image into sharp focus. If you have a binocular microscope, the eyepieces should be adjusted to compensate for eye differences.

Anyone who has used binoculars should find it easy to adjust the oculars on a binocular microscope. Before even focusing on a specimen, you should be able to adjust for eye separation so you will see a single field of view. When the oculars are separated to match your eyes, you should be able to look into them with both eyes relaxed, just as if you are looking across a room. If you have trouble with binocular vision, you could be among the minority of users with eyes set close together, making such viewing difficult. It is  more likely, though, that the individual oculars are simply out of adjustment, which prevents you from bringing the image into focus for both eyes at the same time.

Your microscope may be equipped with one fixed and one adjustable eyepiece, or with both eyepieces adjustable. Either way, the first step is to place each adjustable eyepiece in the center of its range of travel, giving you the most latitude for adjustment either way. The next step is to obtain an image at high enough magnification so that you can see fine details. Step three is to observe with the fixed eyepiece only (or one of the two adjustable eyepieces) with the appropriate eye, and focus the microscope on the image. Recalling one or two specific details from the image, observe with the other eye only, and this time, adjust only the eyepiece until the details come into focus. From this point on, when you focus the microscope, you should be able to look comfortably using both eyes.
If you had trouble seeing a single image when adjusting for eye separation, it may be worth trying again once the oculars are adjusted to match your eyes.