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UCL Home  /  Geography  /  Resources  /  Laboratory  /  Light Microscopy  /  Adjustment of the Interpupillary Distance

Adjustment of the Interpupillary Distance

The interpupillary distance is the distance between the centers of your two pupils. The distance between the two eyepieces of the binocular microscope must correspond to your interpupillary distance. Each person has his or her own interpupillary distance and the microscope must be adjusted for your specific distance. This is true of any binocular microscope. During your first session with a new microscope you must determine the correct interpupillary distance and set the microscope for that distance. During all subsequent sessions you must ascertain that the microscope's interpupillary distance is the correct one for you and adjust it if it is not.

If you look through the eyepieces and see two images, the interpupillary distance is not correct. To correct it, slide the eyepieces closer together or farther apart until the two fields merge to form a single circle of light. The interpupillary distance is now correct for you.

Adjustment of the Diopter Setting

The focal lengths of the two eyepieces must be adjusted to conform to differences, if any, between your two eyes so that the images in both eyepieces are in focus simultaneously. Each eyepiece is equipped with a diopter adjustment ring by which it can be focused independently of the other eyepiece.

1. Adjust the interpupillary distance until it is correct for you.
2. With a test slide in position on the stage, rotate the 10X ocular lens into position.
3. Rotate the dipopter adjustment ring (= tube length adjustment ring) of the left eyepiece until its numerical value is the same as your interpupillary distance.
4. Close your right eye and bring an object into clear sharp focus using the coarse and fine adjustment, as needed.
5. Close your left eye and bring the same object into focus using the diopter ring of the right eyepiece.

My thanks go to David R. Caprette (, Rice University, for allowing me to use the information from his web site to prepare these pages.