PRINCIPLES OF MICROSCOPY

BASIC SETTINGS FOR MICROSCOPE USE: Köhler ILLUMINATION

1. Completely close the field iris diaphragm in the microscope foot.
2. Lower specimen and focus on specimen: Place a specimen on the object plate and focus by adjusting the focal settings. Do not worry about other aspects of image quality at this stage.
3. Focus the field iris diaphragm by adjusting the height of the condenser.
4. Using the two centring screws on the condenser, bring the sharp image into the centre.
5. Open the field iris diaphragm, then only the observed section of the specimen is illuminated. This largely prevents any disturbing stray light and protects the specimen against excessive exposure to light.
6. Adjust lighting equipment: Open the aperture on the condenser until the optimum image characteristics are achieved, i.e. resolution and contrast.

ADJUSTING THE PHASE CONTRAST:

The annular diaphragm and the phase ring must be precisely aligned to achieve an optimal image. A focus scope can be used to check this but is not absolutely necessary.

Using two adjusting screws on the condenser, the annular diaphragm can be positioned and thus brought in alignment with the phase ring. (IMPORTANT: do not confuse with the adjusting screws for centring the entire condenser!)

View of the rear focal plane of the lens: Phase ring (grey) and annular diaphragm are congruent.
View of the rear focal plane of the lens: Phase ring (grey) and annular diaphragm are not congruent.