How to Adjust the Microscope Condenser

Basic Concept

The condenser is usually installed under the microscope stage. Its role is to make up for the lack of light and appropriately change the nature of the light emitted from the light source, focusing the light on the object to be inspected to obtain the best lighting effect.

The condenser is usually composed of a condenser lens, an iridescent aperture and a lifting spiral, and can be divided into a bright field condenser and a dark field condenser.

Ordinary optical microscopes are equipped with bright field condensers, and bright field condensers include Abbe condensers, Qiming condensers and swing-out condensers.

Abbe condensers exhibit chromatic and spherical aberration for objectives with numerical apertures above 0.6. The Qi Ming condenser has a high degree of correction for chromatic aberration, spherical aberration and coma aberration, and is the best quality condenser in bright field microscopy, but it is not suitable for objectives less than 4 times. Swing out the condenser can shake the upper lens of the condenser out of the optical path to meet the needs of low magnification objective lens (4×) large field of view illumination.

Adjustable Range

The condenser is usually installed under the stage, and its function is to focus the light reflected by the light source through the mirror on the sample, so as to obtain the strongest illumination and make the object image bright and clear. The height of the condenser can be adjusted so that the focus falls on the object to obtain the maximum brightness. Generally, the focus of the condenser is 1.25mm above it, and its rising limit is 0.1mm below the plane of the stage. Therefore, it is required that the thickness of the slide glass used should be between 0.8-1.2 mm, otherwise the sample to be inspected is not in focus, which will affect the effect of microscope inspection.

There is also an iridescent aperture in front of the front lens group of the condenser, which can be enlarged and reduced, which affects the resolution and contrast of imaging. If the iris aperture is opened too large and exceeds the numerical aperture of the objective lens, spots will be generated; if the iris aperture is shrunk too small, the resolution will decrease and the contrast will increase. Therefore, when observing, through the adjustment of the iridescent aperture, the field diaphragm (microscope with the field diaphragm) is opened to the circumscribed part of the periphery of the field of view, so that objects not in the field of view cannot receive any light. Lighting to avoid interference from scattered light.

Condenser Adjustment Procedure

Step 1: Bring up the clear polygons

Adjust the field diaphragm and aperture diaphragm to the minimum state. If the state of the microscope is correct, a polygon with clear edges should be visible in the field of view at this time. If what you see is not a polygon with clear edges, it means that the upper and lower positions of the condenser in the optical path are not accurate. At this time, turn the up and down adjustment knob of the condenser to make the condenser rise or fall slowly, so that a polygon with clear edges is formed in the field of view.

Note: Do not adjust the height of the condenser frequently. After adjusting the height, do not move its height position in the future. After the microscope is installed, most of the heights have been adjusted, so the next step can be directly adjusted. (Sometimes if you can't find the polygon, you can zoom in on the field stop a little and you'll be able to find it in slightly brighter conditions.)

Step 2: Center the polygon

The correct position of the polygon in the field of view should be in the center of the field of view. If it is not, it means that the optical path has shifted. It is necessary to adjust the condenser centering screw, that is, the two silver knobs, so that the polygon is in the center of the field of view.

Step 3: Circumscribe the polygon

Slowly enlarge the field diaphragm. When the polygon just circumscribes the field of view, it is the best working position of the field diaphragm. In this way, the optical axis of the condenser is adjusted to be coaxial with the optical axes of the illumination optical path and the imaging optical path. After adjustment, do not mess with the centering screw rod in daily use.

Adjustment of the aperture diaphragm: The outer edge of the condenser of the research microscope has engraved numbers and positioning marks, which is convenient for adjusting the condenser to match the numerical aperture of the objective lens. However, some condensers do not have numbers marked on the outside. In this way, first focus the objective lens, then remove an eyepiece, and look into the lens barrel with your eyes. You can see that the rear lens of the objective lens is a bright circle. If you cannot see the outline image of the aperture stop , indicating that the opening is too large; if it is only a small bright outline image, it means that the shrinking is too small. When it is slowly increased and just forms a bright circle with the rear lens of the objective lens, then the numerical aperture of the condenser lens and the objective lens have been compared with each other. match.

Step 4: Adjusting the Numerical Aperture of the Condenser

Adjust the numerical aperture of the condenser to make a proper match with the numerical aperture of the objective lens to obtain the best resolution. Numerical aperture is closely related to resolution, so the numerical aperture of the condenser should match that of the objective lens. For example: an objective lens with a low numerical aperture should be matched with a condenser with a low numerical aperture, and an oil lens with a high numerical aperture should be matched with a condenser with a high numerical aperture. Only in this way can the resolution of the image be improved.