The transmitted light microscope. (Click on image to view larger version.)

1. Place the mounted specimen on the stage. The area to be viewed should be positioned approximately beneath the objective lens.
2. Switch on the illumination, starting at a low power setting and gradually increase until the desired light level is reached. This can best be judged by increasing the power until a clear spot of light is seen on the specimen surface.
3. Use the lowest magnification objective lens to coarsely focus the microscope. Without looking down the microscope, lower the objective lens close to the specimen surface then use the coarse focus knob to slowly raise it until the circle of light on the specimen appears reasonably sharp.

   Be careful not to 'crash' the lens into the specimen when focusing - ALWAYS focus coarsely by pulling the lens AWAY from the sample.

   The following instructions assume the user is working with a binocular microscope - one with two eyepieces.

4. Adjust the eyepieces so that they are the right distance apart. This is done by carefully sliding them apart or closer together so that a single image can be seen comfortably.
5. Looking through the eyepieces, use the fine focus knob to bring the image into sharp focus.
6. The eyepieces should now be further adjusted - one of them will focus separately, as many people have slightly different focus in each eye. The image should be brought into focus in the non adjustable eyepiece first using the fine focus knob, and then the other eyepiece rotated so that it is also in focus.
7. If a higher magnification is required the appropriate lens can be moved into place, and the image can be refocused using the fine focus knob.

If focus is lost while at a high magnification, do not adjust the focus using the coarse focus knob, as it would be easy to crash the lens into the specimen. Change the objective lens to a lower magnification and then re-focus as described previously. The magnification can be increased again once the specimen is back in focus.

Further tips for transmission microscopy

When using a transmission microscope, it is useful to centre the stage below the lens. This is because it is often necessary to rotate the stage in order to observe changes that occur in polarised light. If the stage is not properly centred, it will be difficult to observe a particular area of the specimen at different angles of rotation.

The stage can be centred by adjusting small knobs at the side of the stage which can move it from side to side and towards and away from the microscope. It should not be necessary to make large adjustments to these knobs.