The Stereo Dissection Microscope

The dissecting microscope is configured to allow low magnification of three-dimensional objects- objects larger or thicker than the compound microscope can accommodate. Furthermore, the two separate lenses of the binocular dissecting microscope allow one to see objects in three dimensions, i.e., in stereo. Dissecting microscopes do not magnify to the extent of compound microscopes. The microscope models we have in the Biology Department magnify from about 10X up to 40X with either variable or zoom magnification.

Illumination

Dissecting microscopes utilize two types of light: from incident light (direct illumination) or from transmitted light. Opaque objects placed on the microscope stage can be directly illuminated with incident light from an illuminator. In this case the illuminator can be mounted in an opening in the arm of the microscope, or in an adapter ring attached to a separate illuminator base (transformer). Alternatively, light from a source such as a lamp can be reflected through a translucent object from underneath using the substage mirror. This method of illumination requires the clear glass insert in the microscope stage. However, in most instances the opaque stage insert, which has a white side and a black side, and direct lighting is most commonly used. You likely will see different types of illuminators avalable in lab.

Procedure

  1. ALWAYS carry the microscope with TWO HANDS. This practice helps prevent bumping and dropping accidents that jar lenses out of alignment. Grasp the microscope arm with one hand and support the microscope under the base with the other hand.
    Remove the dust cover and put it in the microscope cabinet.
  2. Obtain a suitable specimen (object) to view, and place it in a shallow container on the stage.

  1.  Position the illuminator next to the microscope directing the beam at the specimen, and turn it on. Many illuminators have rheostats to allow adjustment of the intensity of the light. Do not use more light than you need, as the image quality will degrade.
 

  1. Adjust the magnification to its lowest power with the magnification knob on the top or side of the microscope body.
  2. Adjust the interpupillary distance of the ocular lenses. Look through the ocular lenses. If you see one image, no adjustment is necessary. If you see two images, or a lot of black, adjust the distance between the ocular tubes until you see one image. You also may need to move your eyes closer to or farther away from the ocular lenses so that the specimen's image fills the lenses.

You may need to adjust the ocular lenses far apart or close together.    

  1. Focus on the specimen. This is a two-step process. In the first step, you will roughly focus on the specimen with the objective lens. In the second step, you will compensate for any differences in strength between your eyes to obtain the sharpest image possible.
  2. Rough focus
    a. Lower the microscope body to its lowest point with the focusing knob on the sides of the microscope arm. Use the focus knob to raise the microscope body until the specimen image is the sharpest.
    Compensation
    b. Compensate for any differences in strength between your eyes. (The following directions are written for microscopes with diopter adjustment rings on the right ocular tube. Obviously, if you have a scope with the diopter adjustment on the left ocular tube, you will start with your right eye closed.)
    c. Close your left eye. Adjust the diopter adjustment ring until the image is in focus for your right eye. You may want to adjust the ring back and forth (i.e., in and out of focus) a few times until you are sure you have the best focus for yourself.
    d. The first time through the diopter adjustment you may want to repeat steps a through d-sometimes our eyes automatically compensate for out-of-focus images seen in the microscope, and eyestrain results. Who wants a headache in bio lab??
  3. If you change the magnification, you may need to adjust the focus again.

When you are finished using the microscope:

  • Turn off the illuminator. Unplug it, lightly wrap the cord around it, and put it in the microscope cabinet.
  • Clean the microscope stage - this is especially critical if you have viewing marine specimens or have used corrosive chemicals in your labwork.
  • Lower the microscope body all the way down.
  • Replace the dust cover.
  • Return the microscope to the cabinet with two hands.
 

Created by Kathy Claerr 1-9-2003
Department of Biology, Bates College, Lewiston, ME 04240