Nikon L-Ke manual Light Source, Condenser Focusing Knob, Brightness Adjustment

small light bundles, the effects by diffraction, reflection, refraction, etc., may be exaggerated so that fringes may be seen at the image edges which may likely induce misinterpretation of the image, but it may be effective for special occassions (e.g. definition of general structure of non stained specimens). (Fig. 8, c).

2.Light Source

As already cited, the iris diaphragm plays an important role In the illumi- nation on microscopy. As a principle the diaphragm should be so adjusted that the numerical aperture of the condenser is equal to that of the objective being used, in order to obtain the maximum resolution. In practice, however, to keep out stray light which would reduce image contrast, closing the aperture of the condenser down to 6 0 - 70% of that of the objec- tive lens will bring about a good result in most cases. The coincidence of condenser diaphragm aperture with the opening (exit pupil) of the objec- tive can be ascertained by looking through the microscope tube after re- moving the eyepiece and closing the diaphragm slowly. An experienced

user, however, may dispense with such a procedure, and will obtain the same result by adjusting the diaphragm opening until satisfactory distinct- ness of the image is obtained.

If a high resolution and, at the same time, a high contrast are desirable, oblique illumination will be effective. This is suited especially for lowdyed specimens, transparent phase-contrast specimens, etc. However, in this illumination, a remarkable polarity in contrast and resolution may appear; it is necessary for observation to change the direction of illumination, by turning the iris diaphragm.

The condenser aperture is off-centered in any direction by rotating and at the same time by radially sliding the diaphragm. This manipulation can be done only by using one hand, the thumb and the first finger for off-centering and the middle finger for opening or closing the diaphragm. (See Fig. 9).

3. Condenser Focusing Knob

The condenser focusing is made by turning the condenser focusing knob. This manipulation is necessary only in case of Koehler illumination or dark

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field observation. The condenser is usually to stay at the upper limit and need not to be lowered, except when a stray image of an outside object superimposes the specimen image too sharply in such a case as in direct sun light illumination or as some uneven brightness interferes with the observation.

4.Brightness Adjustment

For this purpose adjust the voltage of current supply by regulating the transformer of the illuminator or by using a proper neutral density filter. Adjustment by means of the condenser diaphragm is not at all possible.

5.Preparation and Adjustment

(1)Lamp and Socket

As shown in Fig. 10, lining up the red dot on the socket retaining ring to that on the lamp housing, fit the socket to the housing by bayonet fashion.

(2)Centering and Focusing of the Lamp

Bring the illumination change-over lever in the position " M " . Stop down the condenser diaphragm beneath the microscope stage. Move the lamp back and forth to bring the image of the filament into sharp focus on the bottom sur- face of the diaphragm. For this purpose, it is conve- nient to utilize the reflection on the accessory reflecting

mirror, as shown in Fig. 11. Then, turn right or left only the socket

ring to fasten the lamp socket in position.

Bring the illumination change-over lever to the position " H " . Manipu- lating the lamp centering screws, make centering of the image on the condenser diaphragm.

(3)Centering of the Illumination Field Diaphragm

Stop down the opening of the illumination field diaphragm to about 2mm in diameter.

Viewing through the microscope, focus the objective 40X to the image of specimen.

Moving up and down the condenser, make a sharp focused image of the illumination field diaphragm on the specimen.

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