Concentrator, also known as light collectorLocated on the condenser bracket below the specimen. It is mainly composed of a condenser lens and a variable aperture, among which the condenser lens can be divided intoBright field spotlight (standard microscope configuration) and dark field spotlight。2px'>

1. Main parameters of the optical mirror
　　Numerical aperture (NA)It is the main parameter of the spotlight, with a maximum numerical aperture generally ranging from 1.2 to 1.4. The numerical aperture has a certain range of variability, and the number engraved on the upper lens frame usually represents the maximum numerical aperture. By adjusting the opening degree of the lower variable aperture, various different numerical apertures below this number can be obtained to meet the needs of different objective lenses. Some spotlights are composed of several sets of lenses, and the top set of lenses can be removed or moved out of the optical path to reduce the numerical aperture of the spotlight, in order to adapt to the illumination when observing with a low magnification objective lens.

2. The function of a spotlight
The function of a spotlightEquivalent to a convex lens, it acts as a converging light to enhance the illumination of the specimen. Generally, the focal point of a spotlight is designed to be approximately 1.25mm above the lens plane at its upper end.
(The focal point is on the specimen to be observed, and the thickness of the glass slide is about 1.1mm)

3. Variable aperture
irisAlso known as aperture, it is located below the spotlight and consists of more than ten thin metal sheets, with a circular hole formed in the center. Its function is to adjust the light intensity and make the numerical aperture of the condenser lens compatible with the numerical aperture of the objective lens. The larger the aperture of the variable aperture, the larger the numerical aperture (after observation, the aperture should be adjusted to the maximum).
Under the variable aperture, there is also a circular filter holder.

explain:In the middle school laboratory, only the teacher's microscope 1600 is equipped with a condenser, while the student's microscope 640 x is equipped with a rotating light bar. A circular disk that can rotate in a circular motion and is tightly attached to the stage. The rotating light bar (also known as a shutter) has circular holes of varying sizes on the light bar, called aperture.
The diameters are 2, 3, 6, 12, and 16mm respectively. By rotating the light bar, each aperture on the light bar can be aligned with the light hole, and the intensity of the light can be adjusted by varying the size of the aperture.

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