The condenser lens is mounted below the stage. Small microscopes often do not have a condenser. When using an objective lens with a numerical aperture of 0.40 or more, a condenser must be provided. The condenser lens can not only make up for the lack of light quantity and properly change the properties of the light from the light source, but also focus the light on the inspected object to obtain the best lighting effect.
There are various structures of the condenser lens, and the requirements for the condenser lens are also different according to the numerical aperture of the objective lens.
1. Abbe condenser
It was designed by Ernst Abbe, a master at the German Optical University. The Abbe condenser is composed of two lenses and has good light-gathering ability, but when the numerical aperture of the objective lens is higher than 0.60, the chromatic aberration and spherical aberration will appear. Therefore, it is mostly used on ordinary microscopes.
2. Achromatic aplanatic condenser
This kind of condenser, also known as "aspherical condenser" and "Qiming condenser", is composed of a series of lenses. It has a high degree of correction of chromatic aberration and spherical aberration, and can obtain ideal images, which are of high quality in bright field microscopy. The highest kind of condenser, its NA value reaches 1.4. Therefore, advanced research microscopes are often equipped with such condensers. It is not suitable for low magnification objectives below 4 X, otherwise the illumination source cannot fill the entire field of view.
3. Swing out condenser
When using a low magnification objective lens (such as 4X), due to the large field of view, the light cone formed by the light source cannot fill the entire field of view, resulting in a dark edge part of the field of view, and only the central part is illuminated. To fill the field of view with illumination, swing the upper lens of the condenser out of the light path.
4. Other condensers
In addition to the above-mentioned types of condensers used in brightfield, there are also condensers for special purposes. Such as dark field condensers, phase contrast condensers, polarized condensers, differential interference condensers, etc. The above condensers are suitable for corresponding observation methods.
